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Message-ID: <20240910164358.q3ytpik3qr4ovd3e@hu-akhilpo-hyd.qualcomm.com>
Date: Tue, 10 Sep 2024 22:13:58 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Connor Abbott <cwabbott0@...il.com>
CC: Antonino Maniscalco <antomani103@...il.com>,
        Rob Clark
	<robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        "Dmitry Baryshkov" <dmitry.baryshkov@...aro.org>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Daniel
 Vetter" <daniel@...ll.ch>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jonathan Corbet <corbet@....net>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        Sharat Masetty <smasetty@...eaurora.org>,
        "Neil
 Armstrong" <neil.armstrong@...aro.org>
Subject: Re: [PATCH v3 04/10] drm/msm/A6xx: Implement preemption for A7XX
 targets

On Mon, Sep 09, 2024 at 01:22:22PM +0100, Connor Abbott wrote:
> On Fri, Sep 6, 2024 at 9:03 PM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
> >
> > On Thu, Sep 05, 2024 at 04:51:22PM +0200, Antonino Maniscalco wrote:
> > > This patch implements preemption feature for A6xx targets, this allows
> > > the GPU to switch to a higher priority ringbuffer if one is ready. A6XX
> > > hardware as such supports multiple levels of preemption granularities,
> > > ranging from coarse grained(ringbuffer level) to a more fine grained
> > > such as draw-call level or a bin boundary level preemption. This patch
> > > enables the basic preemption level, with more fine grained preemption
> > > support to follow.
> > >
> > > Signed-off-by: Sharat Masetty <smasetty@...eaurora.org>
> > > Signed-off-by: Antonino Maniscalco <antomani103@...il.com>
> > > Tested-by: Neil Armstrong <neil.armstrong@...aro.org> # on SM8650-QRD
> > > ---
> > >  drivers/gpu/drm/msm/Makefile              |   1 +
> > >  drivers/gpu/drm/msm/adreno/a6xx_gpu.c     | 293 +++++++++++++++++++++-
> > >  drivers/gpu/drm/msm/adreno/a6xx_gpu.h     | 161 ++++++++++++
> > >  drivers/gpu/drm/msm/adreno/a6xx_preempt.c | 391 ++++++++++++++++++++++++++++++
> > >  drivers/gpu/drm/msm/msm_ringbuffer.h      |   7 +
> > >  5 files changed, 844 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> > > index f5e2838c6a76..32e915109a59 100644
> > > --- a/drivers/gpu/drm/msm/Makefile
> > > +++ b/drivers/gpu/drm/msm/Makefile
> > > @@ -23,6 +23,7 @@ adreno-y := \
> > >       adreno/a6xx_gpu.o \
> > >       adreno/a6xx_gmu.o \
> > >       adreno/a6xx_hfi.o \
> > > +     adreno/a6xx_preempt.o \
> > >
> > >  adreno-$(CONFIG_DEBUG_FS) += adreno/a5xx_debugfs.o \
> > >
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > index 32a4faa93d7f..ed0b138a2d66 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > @@ -16,6 +16,83 @@
> > >
> > >  #define GPU_PAS_ID 13
> > >
> > > +/* IFPC & Preemption static powerup restore list */
> > > +static const uint32_t a7xx_pwrup_reglist[] = {
> > > +     REG_A6XX_UCHE_TRAP_BASE,
> > > +     REG_A6XX_UCHE_TRAP_BASE + 1,
> > > +     REG_A6XX_UCHE_WRITE_THRU_BASE,
> > > +     REG_A6XX_UCHE_WRITE_THRU_BASE + 1,
> > > +     REG_A6XX_UCHE_GMEM_RANGE_MIN,
> > > +     REG_A6XX_UCHE_GMEM_RANGE_MIN + 1,
> > > +     REG_A6XX_UCHE_GMEM_RANGE_MAX,
> > > +     REG_A6XX_UCHE_GMEM_RANGE_MAX + 1,
> > > +     REG_A6XX_UCHE_CACHE_WAYS,
> > > +     REG_A6XX_UCHE_MODE_CNTL,
> > > +     REG_A6XX_RB_NC_MODE_CNTL,
> > > +     REG_A6XX_RB_CMP_DBG_ECO_CNTL,
> > > +     REG_A7XX_GRAS_NC_MODE_CNTL,
> > > +     REG_A6XX_RB_CONTEXT_SWITCH_GMEM_SAVE_RESTORE,
> > > +     REG_A6XX_UCHE_GBIF_GX_CONFIG,
> > > +     REG_A6XX_UCHE_CLIENT_PF,
> >
> > REG_A6XX_TPL1_DBG_ECO_CNTL1 here. A friendly warning, missing a register
> > in this list (and the below list) will lead to a very frustrating debug.
> >
> > > +};
> > > +
> > > +static const uint32_t a7xx_ifpc_pwrup_reglist[] = {
> > > +     REG_A6XX_TPL1_NC_MODE_CNTL,
> > > +     REG_A6XX_SP_NC_MODE_CNTL,
> > > +     REG_A6XX_CP_DBG_ECO_CNTL,
> > > +     REG_A6XX_CP_PROTECT_CNTL,
> > > +     REG_A6XX_CP_PROTECT(0),
> > > +     REG_A6XX_CP_PROTECT(1),
> > > +     REG_A6XX_CP_PROTECT(2),
> > > +     REG_A6XX_CP_PROTECT(3),
> > > +     REG_A6XX_CP_PROTECT(4),
> > > +     REG_A6XX_CP_PROTECT(5),
> > > +     REG_A6XX_CP_PROTECT(6),
> > > +     REG_A6XX_CP_PROTECT(7),
> > > +     REG_A6XX_CP_PROTECT(8),
> > > +     REG_A6XX_CP_PROTECT(9),
> > > +     REG_A6XX_CP_PROTECT(10),
> > > +     REG_A6XX_CP_PROTECT(11),
> > > +     REG_A6XX_CP_PROTECT(12),
> > > +     REG_A6XX_CP_PROTECT(13),
> > > +     REG_A6XX_CP_PROTECT(14),
> > > +     REG_A6XX_CP_PROTECT(15),
> > > +     REG_A6XX_CP_PROTECT(16),
> > > +     REG_A6XX_CP_PROTECT(17),
> > > +     REG_A6XX_CP_PROTECT(18),
> > > +     REG_A6XX_CP_PROTECT(19),
> > > +     REG_A6XX_CP_PROTECT(20),
> > > +     REG_A6XX_CP_PROTECT(21),
> > > +     REG_A6XX_CP_PROTECT(22),
> > > +     REG_A6XX_CP_PROTECT(23),
> > > +     REG_A6XX_CP_PROTECT(24),
> > > +     REG_A6XX_CP_PROTECT(25),
> > > +     REG_A6XX_CP_PROTECT(26),
> > > +     REG_A6XX_CP_PROTECT(27),
> > > +     REG_A6XX_CP_PROTECT(28),
> > > +     REG_A6XX_CP_PROTECT(29),
> > > +     REG_A6XX_CP_PROTECT(30),
> > > +     REG_A6XX_CP_PROTECT(31),
> > > +     REG_A6XX_CP_PROTECT(32),
> > > +     REG_A6XX_CP_PROTECT(33),
> > > +     REG_A6XX_CP_PROTECT(34),
> > > +     REG_A6XX_CP_PROTECT(35),
> > > +     REG_A6XX_CP_PROTECT(36),
> > > +     REG_A6XX_CP_PROTECT(37),
> > > +     REG_A6XX_CP_PROTECT(38),
> > > +     REG_A6XX_CP_PROTECT(39),
> > > +     REG_A6XX_CP_PROTECT(40),
> > > +     REG_A6XX_CP_PROTECT(41),
> > > +     REG_A6XX_CP_PROTECT(42),
> > > +     REG_A6XX_CP_PROTECT(43),
> > > +     REG_A6XX_CP_PROTECT(44),
> > > +     REG_A6XX_CP_PROTECT(45),
> > > +     REG_A6XX_CP_PROTECT(46),
> > > +     REG_A6XX_CP_PROTECT(47),
> > > +     REG_A6XX_CP_AHB_CNTL,
> > > +};
> > > +
> > > +
> > >  static inline bool _a6xx_check_idle(struct msm_gpu *gpu)
> > >  {
> > >       struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > @@ -68,6 +145,8 @@ static void update_shadow_rptr(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > >
> > >  static void a6xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > >  {
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > >       uint32_t wptr;
> > >       unsigned long flags;
> > >
> > > @@ -81,12 +160,26 @@ static void a6xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > >       /* Make sure to wrap wptr if we need to */
> > >       wptr = get_wptr(ring);
> > >
> > > -     spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > > -
> > >       /* Make sure everything is posted before making a decision */
> > >       mb();
> >
> > This looks unnecessary.
> >
> > >
> > > -     gpu_write(gpu, REG_A6XX_CP_RB_WPTR, wptr);
> > > +     /* Update HW if this is the current ring and we are not in preempt*/
> > > +     if (!a6xx_in_preempt(a6xx_gpu)) {
> > > +             /*
> > > +              * Order the reads of the preempt state and cur_ring. This
> > > +              * matches the barrier after writing cur_ring.
> > > +              */
> > > +             rmb();
> >
> > we can use the lighter smp variant here.
> >
> > > +
> > > +             if (a6xx_gpu->cur_ring == ring)
> > > +                     gpu_write(gpu, REG_A6XX_CP_RB_WPTR, wptr);
> > > +             else
> > > +                     ring->skip_inline_wptr = true;
> > > +     } else {
> > > +             ring->skip_inline_wptr = true;
> > > +     }
> > > +
> > > +     spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > >  }
> > >
> > >  static void get_stats_counter(struct msm_ringbuffer *ring, u32 counter,
> > > @@ -138,12 +231,14 @@ static void a6xx_set_pagetable(struct a6xx_gpu *a6xx_gpu,
> >
> > set_pagetable checks "cur_ctx_seqno" to see if pt switch is needed or
> > not. This is currently not tracked separately for each ring. Can you
> > please check that?
> >
> > I wonder why that didn't cause any gpu errors in testing. Not sure if I
> > am missing something.
> >
> > >
> > >       /*
> > >        * Write the new TTBR0 to the memstore. This is good for debugging.
> > > +      * Needed for preemption
> > >        */
> > > -     OUT_PKT7(ring, CP_MEM_WRITE, 4);
> > > +     OUT_PKT7(ring, CP_MEM_WRITE, 5);
> > >       OUT_RING(ring, CP_MEM_WRITE_0_ADDR_LO(lower_32_bits(memptr)));
> > >       OUT_RING(ring, CP_MEM_WRITE_1_ADDR_HI(upper_32_bits(memptr)));
> > >       OUT_RING(ring, lower_32_bits(ttbr));
> > > -     OUT_RING(ring, (asid << 16) | upper_32_bits(ttbr));
> > > +     OUT_RING(ring, upper_32_bits(ttbr));
> > > +     OUT_RING(ring, ctx->seqno);
> > >
> > >       /*
> > >        * Sync both threads after switching pagetables and enable BR only
> > > @@ -268,6 +363,43 @@ static void a6xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > >       a6xx_flush(gpu, ring);
> > >  }
> > >
> > > +static void a6xx_emit_set_pseudo_reg(struct msm_ringbuffer *ring,
> > > +             struct a6xx_gpu *a6xx_gpu, struct msm_gpu_submitqueue *queue)
> > > +{
> > > +     u64 preempt_offset_priv_secure;
> > > +
> > > +     OUT_PKT7(ring, CP_SET_PSEUDO_REG, 15);
> > > +
> > > +     OUT_RING(ring, SMMU_INFO);
> > > +     /* don't save SMMU, we write the record from the kernel instead */
> > > +     OUT_RING(ring, 0);
> > > +     OUT_RING(ring, 0);
> > > +
> > > +     /* privileged and non secure buffer save */
> > > +     OUT_RING(ring, NON_SECURE_SAVE_ADDR);
> > > +     OUT_RING(ring, lower_32_bits(
> > > +             a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE));
> > > +     OUT_RING(ring, upper_32_bits(
> > > +             a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE));
> > > +     OUT_RING(ring, SECURE_SAVE_ADDR);
> > > +     preempt_offset_priv_secure =
> > > +             PREEMPT_OFFSET_PRIV_SECURE(a6xx_gpu->base.info->preempt_record_size);
> > > +     OUT_RING(ring, lower_32_bits(
> > > +             a6xx_gpu->preempt_iova[ring->id] + preempt_offset_priv_secure));
> > > +     OUT_RING(ring, upper_32_bits(
> > > +             a6xx_gpu->preempt_iova[ring->id] + preempt_offset_priv_secure));
> > > +
> > > +     /* user context buffer save, seems to be unnused by fw */
> > > +     OUT_RING(ring, NON_PRIV_SAVE_ADDR);
> > > +     OUT_RING(ring, 0);
> > > +     OUT_RING(ring, 0);
> > > +
> > > +     OUT_RING(ring, COUNTER);
> > > +     /* seems OK to set to 0 to disable it */
> > > +     OUT_RING(ring, 0);
> > > +     OUT_RING(ring, 0);
> > > +}
> > > +
> > >  static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > >  {
> > >       unsigned int index = submit->seqno % MSM_GPU_SUBMIT_STATS_COUNT;
> > > @@ -283,6 +415,13 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > >       OUT_PKT7(ring, CP_THREAD_CONTROL, 1);
> > >       OUT_RING(ring, CP_THREAD_CONTROL_0_SYNC_THREADS | CP_SET_THREAD_BR);
> > >
> > > +     /*
> > > +      * If preemption is enabled, then set the pseudo register for the save
> > > +      * sequence
> > > +      */
> > > +     if (gpu->nr_rings > 1)
> > > +             a6xx_emit_set_pseudo_reg(ring, a6xx_gpu, submit->queue);
> >
> > Can we move this after set_pagetable()?
> >
> > > +
> > >       a6xx_set_pagetable(a6xx_gpu, ring, submit->queue->ctx);
> > >
> > >       get_stats_counter(ring, REG_A7XX_RBBM_PERFCTR_CP(0),
> > > @@ -376,6 +515,8 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > >       OUT_RING(ring, upper_32_bits(rbmemptr(ring, bv_fence)));
> > >       OUT_RING(ring, submit->seqno);
> > >
> > > +     a6xx_gpu->last_seqno[ring->id] = submit->seqno;
> > > +
> > >       /* write the ringbuffer timestamp */
> > >       OUT_PKT7(ring, CP_EVENT_WRITE, 4);
> > >       OUT_RING(ring, CACHE_CLEAN | CP_EVENT_WRITE_0_IRQ | BIT(27));
> > > @@ -389,10 +530,32 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > >       OUT_PKT7(ring, CP_SET_MARKER, 1);
> > >       OUT_RING(ring, 0x100); /* IFPC enable */
> > >
> > > +     /* If preemption is enabled */
> > > +     if (gpu->nr_rings > 1) {
> > > +             /* Yield the floor on command completion */
> > > +             OUT_PKT7(ring, CP_CONTEXT_SWITCH_YIELD, 4);
> > > +
> > > +             /*
> > > +              * If dword[2:1] are non zero, they specify an address for
> > > +              * the CP to write the value of dword[3] to on preemption
> > > +              * complete. Write 0 to skip the write
> > > +              */
> > > +             OUT_RING(ring, 0x00);
> > > +             OUT_RING(ring, 0x00);
> > > +             /* Data value - not used if the address above is 0 */
> > > +             OUT_RING(ring, 0x01);
> > > +             /* generate interrupt on preemption completion */
> > > +             OUT_RING(ring, 0x00);
> > > +     }
> > > +
> > > +
> > >       trace_msm_gpu_submit_flush(submit,
> > >               gpu_read64(gpu, REG_A6XX_CP_ALWAYS_ON_COUNTER));
> > >
> > >       a6xx_flush(gpu, ring);
> > > +
> > > +     /* Check to see if we need to start preemption */
> > > +     a6xx_preempt_trigger(gpu);
> > >  }
> > >
> > >  static void a6xx_set_hwcg(struct msm_gpu *gpu, bool state)
> > > @@ -588,6 +751,89 @@ static void a6xx_set_ubwc_config(struct msm_gpu *gpu)
> > >                 adreno_gpu->ubwc_config.min_acc_len << 23 | hbb_lo << 21);
> > >  }
> > >
> > > +static void a7xx_patch_pwrup_reglist(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     struct adreno_reglist_list reglist[2];
> > > +     void *ptr = a6xx_gpu->pwrup_reglist_ptr;
> > > +     struct cpu_gpu_lock *lock = ptr;
> > > +     u32 *dest = (u32 *)&lock->regs[0];
> > > +     int i, j;
> > > +
> > This sequence is required only once. We can use a flag to check and bail out
> > next time.
> >
> > > +     lock->gpu_req = lock->cpu_req = lock->turn = 0;
> > > +     lock->ifpc_list_len = ARRAY_SIZE(a7xx_ifpc_pwrup_reglist);
> > > +     lock->preemption_list_len = ARRAY_SIZE(a7xx_pwrup_reglist);
> > > +
> > > +     /* Static IFPC-only registers */
> > > +     reglist[0].regs = a7xx_ifpc_pwrup_reglist;
> > > +     reglist[0].count = ARRAY_SIZE(a7xx_ifpc_pwrup_reglist);
> > > +     lock->ifpc_list_len = reglist[0].count;
> > > +
> > > +     /* Static IFPC + preemption registers */
> > > +     reglist[1].regs = a7xx_pwrup_reglist;
> > > +     reglist[1].count = ARRAY_SIZE(a7xx_pwrup_reglist);
> > > +     lock->preemption_list_len = reglist[1].count;
> > > +
> > > +     /*
> > > +      * For each entry in each of the lists, write the offset and the current
> > > +      * register value into the GPU buffer
> > > +      */
> > > +     for (i = 0; i < 2; i++) {
> > > +             const u32 *r = reglist[i].regs;
> > > +
> > > +             for (j = 0; j < reglist[i].count; j++) {
> > > +                     *dest++ = r[j];
> > > +                     *dest++ = gpu_read(gpu, r[j]);
> > > +             }
> > > +     }
> > > +
> > > +     /*
> > > +      * The overall register list is composed of
> > > +      * 1. Static IFPC-only registers
> > > +      * 2. Static IFPC + preemption registers
> > > +      * 3. Dynamic IFPC + preemption registers (ex: perfcounter selects)
> > > +      *
> > > +      * The first two lists are static. Size of these lists are stored as
> > > +      * number of pairs in ifpc_list_len and preemption_list_len
> > > +      * respectively. With concurrent binning, Some of the perfcounter
> > > +      * registers being virtualized, CP needs to know the pipe id to program
> > > +      * the aperture inorder to restore the same. Thus, third list is a
> > > +      * dynamic list with triplets as
> > > +      * (<aperture, shifted 12 bits> <address> <data>), and the length is
> > > +      * stored as number for triplets in dynamic_list_len.
> > > +      */
> > > +     lock->dynamic_list_len = 0;
> > > +}
> > > +
> > > +static int a7xx_preempt_start(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     struct msm_ringbuffer *ring = gpu->rb[0];
> > > +
> > > +     if (gpu->nr_rings <= 1)
> > > +             return 0;
> > > +
> > > +     /* Turn CP protection off */
> > > +     OUT_PKT7(ring, CP_SET_PROTECTED_MODE, 1);
> > > +     OUT_RING(ring, 0);
> > > +
> > > +     a6xx_emit_set_pseudo_reg(ring, a6xx_gpu, NULL);
> > > +
> > > +     /* Yield the floor on command completion */
> > > +     OUT_PKT7(ring, CP_CONTEXT_SWITCH_YIELD, 4);
> > > +     OUT_RING(ring, 0x00);
> > > +     OUT_RING(ring, 0x00);
> > > +     OUT_RING(ring, 0x01);
> >
> > Looks like kgsl use 0x00 here. Not sure if that matters!
> >
> > > +     /* Generate interrupt on preemption completion */
> > > +     OUT_RING(ring, 0x00);
> > > +
> > > +     a6xx_flush(gpu, ring);
> > > +
> > > +     return a6xx_idle(gpu, ring) ? 0 : -EINVAL;
> > > +}
> > > +
> > >  static int a6xx_cp_init(struct msm_gpu *gpu)
> > >  {
> > >       struct msm_ringbuffer *ring = gpu->rb[0];
> > > @@ -619,6 +865,8 @@ static int a6xx_cp_init(struct msm_gpu *gpu)
> > >
> > >  static int a7xx_cp_init(struct msm_gpu *gpu)
> > >  {
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > >       struct msm_ringbuffer *ring = gpu->rb[0];
> > >       u32 mask;
> > >
> > > @@ -626,6 +874,8 @@ static int a7xx_cp_init(struct msm_gpu *gpu)
> > >       OUT_PKT7(ring, CP_THREAD_CONTROL, 1);
> > >       OUT_RING(ring, BIT(27));
> > >
> > > +     a7xx_patch_pwrup_reglist(gpu);
> > > +
> >
> > Looks out of place. I guess you kept it here to avoid an extra a7x
> > check. At least we should move this before the above pm4 packets.
> >
> > >       OUT_PKT7(ring, CP_ME_INIT, 7);
> > >
> > >       /* Use multiple HW contexts */
> > > @@ -656,11 +906,11 @@ static int a7xx_cp_init(struct msm_gpu *gpu)
> > >
> > >       /* *Don't* send a power up reg list for concurrent binning (TODO) */
> > >       /* Lo address */
> > > -     OUT_RING(ring, 0x00000000);
> > > +     OUT_RING(ring, lower_32_bits(a6xx_gpu->pwrup_reglist_iova));
> > >       /* Hi address */
> > > -     OUT_RING(ring, 0x00000000);
> > > +     OUT_RING(ring, upper_32_bits(a6xx_gpu->pwrup_reglist_iova));
> > >       /* BIT(31) set => read the regs from the list */
> > > -     OUT_RING(ring, 0x00000000);
> > > +     OUT_RING(ring, BIT(31));
> > >
> > >       a6xx_flush(gpu, ring);
> > >       return a6xx_idle(gpu, ring) ? 0 : -EINVAL;
> > > @@ -784,6 +1034,16 @@ static int a6xx_ucode_load(struct msm_gpu *gpu)
> > >               msm_gem_object_set_name(a6xx_gpu->shadow_bo, "shadow");
> > >       }
> > >
> > > +     a6xx_gpu->pwrup_reglist_ptr = msm_gem_kernel_new(gpu->dev, PAGE_SIZE,
> > > +                                                      MSM_BO_WC  | MSM_BO_MAP_PRIV,
> > > +                                                      gpu->aspace, &a6xx_gpu->pwrup_reglist_bo,
> > > +                                                      &a6xx_gpu->pwrup_reglist_iova);
> > > +
> > > +     if (IS_ERR(a6xx_gpu->pwrup_reglist_ptr))
> > > +             return PTR_ERR(a6xx_gpu->pwrup_reglist_ptr);
> > > +
> > > +     msm_gem_object_set_name(a6xx_gpu->pwrup_reglist_bo, "pwrup_reglist");
> > > +
> > >       return 0;
> > >  }
> > >
> > > @@ -1127,6 +1387,8 @@ static int hw_init(struct msm_gpu *gpu)
> > >       if (a6xx_gpu->shadow_bo) {
> > >               gpu_write64(gpu, REG_A6XX_CP_RB_RPTR_ADDR,
> > >                       shadowptr(a6xx_gpu, gpu->rb[0]));
> > > +             for (unsigned int i = 0; i < gpu->nr_rings; i++)
> > > +                     a6xx_gpu->shadow[i] = 0;
> > >       }
> > >
> > >       /* ..which means "always" on A7xx, also for BV shadow */
> > > @@ -1135,6 +1397,8 @@ static int hw_init(struct msm_gpu *gpu)
> > >                           rbmemptr(gpu->rb[0], bv_rptr));
> > >       }
> > >
> > > +     a6xx_preempt_hw_init(gpu);
> > > +
> > >       /* Always come up on rb 0 */
> > >       a6xx_gpu->cur_ring = gpu->rb[0];
> > >
> > > @@ -1180,6 +1444,10 @@ static int hw_init(struct msm_gpu *gpu)
> > >  out:
> > >       if (adreno_has_gmu_wrapper(adreno_gpu))
> > >               return ret;
> > > +
> > > +     /* Last step - yield the ringbuffer */
> > > +     a7xx_preempt_start(gpu);
> > > +
> > >       /*
> > >        * Tell the GMU that we are done touching the GPU and it can start power
> > >        * management
> > > @@ -1557,8 +1825,13 @@ static irqreturn_t a6xx_irq(struct msm_gpu *gpu)
> > >       if (status & A6XX_RBBM_INT_0_MASK_SWFUSEVIOLATION)
> > >               a7xx_sw_fuse_violation_irq(gpu);
> > >
> > > -     if (status & A6XX_RBBM_INT_0_MASK_CP_CACHE_FLUSH_TS)
> > > +     if (status & A6XX_RBBM_INT_0_MASK_CP_CACHE_FLUSH_TS) {
> > >               msm_gpu_retire(gpu);
> > > +             a6xx_preempt_trigger(gpu);
> > > +     }
> > > +
> > > +     if (status & A6XX_RBBM_INT_0_MASK_CP_SW)
> > > +             a6xx_preempt_irq(gpu);
> > >
> > >       return IRQ_HANDLED;
> > >  }
> > > @@ -2331,6 +2604,8 @@ struct msm_gpu *a6xx_gpu_init(struct drm_device *dev)
> > >                               a6xx_fault_handler);
> > >
> > >       a6xx_calc_ubwc_config(adreno_gpu);
> > > +     /* Set up the preemption specific bits and pieces for each ringbuffer */
> > > +     a6xx_preempt_init(gpu);
> > >
> > >       return gpu;
> > >  }
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > > index e3e5c53ae8af..da10060e38dc 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > > @@ -12,6 +12,31 @@
> > >
> > >  extern bool hang_debug;
> > >
> > > +struct cpu_gpu_lock {
> > > +     uint32_t gpu_req;
> > > +     uint32_t cpu_req;
> > > +     uint32_t turn;
> > > +     union {
> > > +             struct {
> > > +                     uint16_t list_length;
> > > +                     uint16_t list_offset;
> > > +             };
> > > +             struct {
> > > +                     uint8_t ifpc_list_len;
> > > +                     uint8_t preemption_list_len;
> > > +                     uint16_t dynamic_list_len;
> > > +             };
> > > +     };
> > > +     uint64_t regs[62];
> > > +};
> > > +
> > > +struct adreno_reglist_list {
> > > +     /** @reg: List of register **/
> > > +     const u32 *regs;
> > > +     /** @count: Number of registers in the list **/
> > > +     u32 count;
> > > +};
> > > +
> > >  /**
> > >   * struct a6xx_info - a6xx specific information from device table
> > >   *
> > > @@ -31,6 +56,20 @@ struct a6xx_gpu {
> > >       uint64_t sqe_iova;
> > >
> > >       struct msm_ringbuffer *cur_ring;
> > > +     struct msm_ringbuffer *next_ring;
> > > +
> > > +     struct drm_gem_object *preempt_bo[MSM_GPU_MAX_RINGS];
> > > +     void *preempt[MSM_GPU_MAX_RINGS];
> > > +     uint64_t preempt_iova[MSM_GPU_MAX_RINGS];
> > > +     uint32_t last_seqno[MSM_GPU_MAX_RINGS];
> > > +
> > > +     atomic_t preempt_state;
> > > +     spinlock_t eval_lock;
> > > +     struct timer_list preempt_timer;
> > > +
> > > +     unsigned int preempt_level;
> > > +     bool uses_gmem;
> > > +     bool skip_save_restore;
> > >
> > >       struct a6xx_gmu gmu;
> > >
> > > @@ -38,6 +77,10 @@ struct a6xx_gpu {
> > >       uint64_t shadow_iova;
> > >       uint32_t *shadow;
> > >
> > > +     struct drm_gem_object *pwrup_reglist_bo;
> > > +     void *pwrup_reglist_ptr;
> > > +     uint64_t pwrup_reglist_iova;
> > > +
> > >       bool has_whereami;
> > >
> > >       void __iomem *llc_mmio;
> > > @@ -49,6 +92,105 @@ struct a6xx_gpu {
> > >
> > >  #define to_a6xx_gpu(x) container_of(x, struct a6xx_gpu, base)
> > >
> > > +/*
> > > + * In order to do lockless preemption we use a simple state machine to progress
> > > + * through the process.
> > > + *
> > > + * PREEMPT_NONE - no preemption in progress.  Next state START.
> > > + * PREEMPT_START - The trigger is evaluating if preemption is possible. Next
> > > + * states: TRIGGERED, NONE
> > > + * PREEMPT_FINISH - An intermediate state before moving back to NONE. Next
> > > + * state: NONE.
> > > + * PREEMPT_TRIGGERED: A preemption has been executed on the hardware. Next
> > > + * states: FAULTED, PENDING
> > > + * PREEMPT_FAULTED: A preemption timed out (never completed). This will trigger
> > > + * recovery.  Next state: N/A
> > > + * PREEMPT_PENDING: Preemption complete interrupt fired - the callback is
> > > + * checking the success of the operation. Next state: FAULTED, NONE.
> > > + */
> > > +
> > > +enum a6xx_preempt_state {
> > > +     PREEMPT_NONE = 0,
> > > +     PREEMPT_START,
> > > +     PREEMPT_FINISH,
> > > +     PREEMPT_TRIGGERED,
> > > +     PREEMPT_FAULTED,
> > > +     PREEMPT_PENDING,
> > > +};
> > > +
> > > +/*
> > > + * struct a6xx_preempt_record is a shared buffer between the microcode and the
> > > + * CPU to store the state for preemption. The record itself is much larger
> > > + * (2112k) but most of that is used by the CP for storage.
> > > + *
> > > + * There is a preemption record assigned per ringbuffer. When the CPU triggers a
> > > + * preemption, it fills out the record with the useful information (wptr, ring
> > > + * base, etc) and the microcode uses that information to set up the CP following
> > > + * the preemption.  When a ring is switched out, the CP will save the ringbuffer
> > > + * state back to the record. In this way, once the records are properly set up
> > > + * the CPU can quickly switch back and forth between ringbuffers by only
> > > + * updating a few registers (often only the wptr).
> > > + *
> > > + * These are the CPU aware registers in the record:
> > > + * @magic: Must always be 0xAE399D6EUL
> > > + * @info: Type of the record - written 0 by the CPU, updated by the CP
> > > + * @errno: preemption error record
> > > + * @data: Data field in YIELD and SET_MARKER packets, Written and used by CP
> > > + * @cntl: Value of RB_CNTL written by CPU, save/restored by CP
> > > + * @rptr: Value of RB_RPTR written by CPU, save/restored by CP
> > > + * @wptr: Value of RB_WPTR written by CPU, save/restored by CP
> > > + * @_pad: Reserved/padding
> > > + * @rptr_addr: Value of RB_RPTR_ADDR_LO|HI written by CPU, save/restored by CP
> > > + * @rbase: Value of RB_BASE written by CPU, save/restored by CP
> > > + * @counter: GPU address of the storage area for the preemption counters
> >
> > doc missing for bv_rptr_addr.
> >
> > > + */
> > > +struct a6xx_preempt_record {
> > > +     u32 magic;
> > > +     u32 info;
> > > +     u32 errno;
> > > +     u32 data;
> > > +     u32 cntl;
> > > +     u32 rptr;
> > > +     u32 wptr;
> > > +     u32 _pad;
> > > +     u64 rptr_addr;
> > > +     u64 rbase;
> > > +     u64 counter;
> > > +     u64 bv_rptr_addr;
> > > +};
> > > +
> > > +#define A6XX_PREEMPT_RECORD_MAGIC 0xAE399D6EUL
> > > +
> > > +#define PREEMPT_RECORD_SIZE_FALLBACK(size) \
> > > +     ((size) == 0 ? 4192 * SZ_1K : (size))
> > > +
> > > +#define PREEMPT_OFFSET_SMMU_INFO 0
> > > +#define PREEMPT_OFFSET_PRIV_NON_SECURE (PREEMPT_OFFSET_SMMU_INFO + 4096)
> > > +#define PREEMPT_OFFSET_PRIV_SECURE(size) \
> > > +     (PREEMPT_OFFSET_PRIV_NON_SECURE + PREEMPT_RECORD_SIZE_FALLBACK(size))
> > > +#define PREEMPT_SIZE(size) \
> > > +     (PREEMPT_OFFSET_PRIV_SECURE(size) + PREEMPT_RECORD_SIZE_FALLBACK(size))
> > > +
> > > +/*
> > > + * The preemption counter block is a storage area for the value of the
> > > + * preemption counters that are saved immediately before context switch. We
> > > + * append it on to the end of the allocation for the preemption record.
> > > + */
> > > +#define A6XX_PREEMPT_COUNTER_SIZE (16 * 4)
> > > +
> > > +#define A6XX_PREEMPT_USER_RECORD_SIZE (192 * 1024)
> >
> > Unused.
> >
> > > +
> > > +struct a7xx_cp_smmu_info {
> > > +     u32 magic;
> > > +     u32 _pad4;
> > > +     u64 ttbr0;
> > > +     u32 asid;
> > > +     u32 context_idr;
> > > +     u32 context_bank;
> > > +};
> > > +
> > > +#define GEN7_CP_SMMU_INFO_MAGIC 0x241350d5UL
> > > +
> > >  /*
> > >   * Given a register and a count, return a value to program into
> > >   * REG_CP_PROTECT_REG(n) - this will block both reads and writes for
> > > @@ -106,6 +248,25 @@ int a6xx_gmu_init(struct a6xx_gpu *a6xx_gpu, struct device_node *node);
> > >  int a6xx_gmu_wrapper_init(struct a6xx_gpu *a6xx_gpu, struct device_node *node);
> > >  void a6xx_gmu_remove(struct a6xx_gpu *a6xx_gpu);
> > >
> > > +void a6xx_preempt_init(struct msm_gpu *gpu);
> > > +void a6xx_preempt_hw_init(struct msm_gpu *gpu);
> > > +void a6xx_preempt_trigger(struct msm_gpu *gpu);
> > > +void a6xx_preempt_irq(struct msm_gpu *gpu);
> > > +void a6xx_preempt_fini(struct msm_gpu *gpu);
> > > +int a6xx_preempt_submitqueue_setup(struct msm_gpu *gpu,
> > > +             struct msm_gpu_submitqueue *queue);
> > > +void a6xx_preempt_submitqueue_close(struct msm_gpu *gpu,
> > > +             struct msm_gpu_submitqueue *queue);
> > > +
> > > +/* Return true if we are in a preempt state */
> > > +static inline bool a6xx_in_preempt(struct a6xx_gpu *a6xx_gpu)
> > > +{
> > > +     int preempt_state = atomic_read(&a6xx_gpu->preempt_state);
> >
> > I think we should keep a matching barrier before the 'read' similar to the one used in the
> > set_preempt_state helper.
> 
> Good idea, but for the one case we found where it matters (the
> a6xx_flush() vs. updating the ring in a6xx_preempt_irq() race) the
> barrier needs to be after the read. The sequence is something like:
> 
> Thread A:
> 
> a6xx_gpu->cur_ring = a6xx_gpu->next_ring;
> a6xx_gpu->preempt_state = PREEMPT_FINISH;
> 
> Thread B:
> 
> read a6xx_gpu->preempt_state;
> read a6xx_gpu->cur_ring;
> 
> And if the read to preempt_state returns PREEMPT_FINISH, then we need
> cur_ring to reflect the ring we switched to. (I discovered this the
> hard way from debugging deadlocks...)
> 
> So, maybe add a smp_rmb() before and after, then drop the explicit
> barrier in a6xx_flush()?

Ack. I think it is better to use a helper similar to set_preempt_state()
and consistently use that everywhere.

> 
> >
> > > +
> > > +     return !(preempt_state == PREEMPT_NONE ||
> > > +                     preempt_state == PREEMPT_FINISH);
> > > +}
> > > +
> > >  void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp,
> > >                      bool suspended);
> > >  unsigned long a6xx_gmu_get_freq(struct msm_gpu *gpu);
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_preempt.c b/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > > new file mode 100644
> > > index 000000000000..1caff76aca6e
> > > --- /dev/null
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > > @@ -0,0 +1,391 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/* Copyright (c) 2018, The Linux Foundation. All rights reserved. */
> > > +/* Copyright (c) 2023 Collabora, Ltd. */
> > > +/* Copyright (c) 2024 Valve Corporation */
> > > +
> > > +#include "msm_gem.h"
> > > +#include "a6xx_gpu.h"
> > > +#include "a6xx_gmu.xml.h"
> > > +#include "msm_mmu.h"
> > > +
> > > +/*
> > > + * Try to transition the preemption state from old to new. Return
> > > + * true on success or false if the original state wasn't 'old'
> > > + */
> > > +static inline bool try_preempt_state(struct a6xx_gpu *a6xx_gpu,
> > > +             enum a6xx_preempt_state old, enum a6xx_preempt_state new)
> > > +{
> > > +     enum a6xx_preempt_state cur = atomic_cmpxchg(&a6xx_gpu->preempt_state,
> > > +             old, new);
> > > +
> > > +     return (cur == old);
> > > +}
> > > +
> > > +/*
> > > + * Force the preemption state to the specified state.  This is used in cases
> > > + * where the current state is known and won't change
> > > + */
> > > +static inline void set_preempt_state(struct a6xx_gpu *gpu,
> > > +             enum a6xx_preempt_state new)
> > > +{
> > > +     /*
> > > +      * preempt_state may be read by other cores trying to trigger a
> > > +      * preemption or in the interrupt handler so barriers are needed
> > > +      * before...
> > > +      */
> > > +     smp_mb__before_atomic();
> > > +     atomic_set(&gpu->preempt_state, new);
> > > +     /* ... and after*/
> > > +     smp_mb__after_atomic();
> > > +}
> > > +
> > > +/* Write the most recent wptr for the given ring into the hardware */
> > > +static inline void update_wptr(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > > +{
> > > +     unsigned long flags;
> > > +     uint32_t wptr;
> > > +
> > > +     if (!ring)
> >
> > Is this ever true?
> >
> > > +             return;
> > > +
> > > +     spin_lock_irqsave(&ring->preempt_lock, flags);
> > > +
> > > +     if (ring->skip_inline_wptr) {
> > > +             wptr = get_wptr(ring);
> > > +
> > > +             gpu_write(gpu, REG_A6XX_CP_RB_WPTR, wptr);
> > > +
> > > +             ring->skip_inline_wptr = false;
> > > +     }
> > > +
> > > +     spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > > +}
> > > +
> > > +/* Return the highest priority ringbuffer with something in it */
> > > +static struct msm_ringbuffer *get_next_ring(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +
> > > +     unsigned long flags;
> > > +     int i;
> > > +
> > > +     for (i = 0; i < gpu->nr_rings; i++) {
> > > +             bool empty;
> > > +             struct msm_ringbuffer *ring = gpu->rb[i];
> > > +
> > > +             spin_lock_irqsave(&ring->preempt_lock, flags);
> > > +             empty = (get_wptr(ring) == gpu->funcs->get_rptr(gpu, ring));
> > > +             if (!empty && ring == a6xx_gpu->cur_ring)
> > > +                     empty = ring->memptrs->fence == a6xx_gpu->last_seqno[i];
> > > +             spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > > +
> > > +             if (!empty)
> > > +                     return ring;
> > > +     }
> > > +
> > > +     return NULL;
> > > +}
> > > +
> > > +static void a6xx_preempt_timer(struct timer_list *t)
> > > +{
> > > +     struct a6xx_gpu *a6xx_gpu = from_timer(a6xx_gpu, t, preempt_timer);
> > > +     struct msm_gpu *gpu = &a6xx_gpu->base.base;
> > > +     struct drm_device *dev = gpu->dev;
> > > +
> > > +     if (!try_preempt_state(a6xx_gpu, PREEMPT_TRIGGERED, PREEMPT_FAULTED))
> > > +             return;
> > > +
> > > +     dev_err(dev->dev, "%s: preemption timed out\n", gpu->name);
> > > +     kthread_queue_work(gpu->worker, &gpu->recover_work);
> > > +}
> > > +
> > > +void a6xx_preempt_irq(struct msm_gpu *gpu)
> > > +{
> > > +     uint32_t status;
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     struct drm_device *dev = gpu->dev;
> > > +
> > > +     if (!try_preempt_state(a6xx_gpu, PREEMPT_TRIGGERED, PREEMPT_PENDING))
> > > +             return;
> > > +
> > > +     /* Delete the preemption watchdog timer */
> > > +     del_timer(&a6xx_gpu->preempt_timer);
> > > +
> > > +     /*
> > > +      * The hardware should be setting the stop bit of CP_CONTEXT_SWITCH_CNTL
> > > +      * to zero before firing the interrupt, but there is a non zero chance
> > > +      * of a hardware condition or a software race that could set it again
> > > +      * before we have a chance to finish. If that happens, log and go for
> > > +      * recovery
> > > +      */
> > > +     status = gpu_read(gpu, REG_A6XX_CP_CONTEXT_SWITCH_CNTL);
> > > +     if (unlikely(status & A6XX_CP_CONTEXT_SWITCH_CNTL_STOP)) {
> > > +             DRM_DEV_ERROR(&gpu->pdev->dev,
> > > +                                       "!!!!!!!!!!!!!!!! preemption faulted !!!!!!!!!!!!!! irq\n");
> > > +             set_preempt_state(a6xx_gpu, PREEMPT_FAULTED);
> > > +             dev_err(dev->dev, "%s: Preemption failed to complete\n",
> > > +                     gpu->name);
> > > +             kthread_queue_work(gpu->worker, &gpu->recover_work);
> > > +             return;
> > > +     }
> > > +
> > > +     a6xx_gpu->cur_ring = a6xx_gpu->next_ring;
> > > +     a6xx_gpu->next_ring = NULL;
> > > +
> > > +     /* Make sure the write to cur_ring is posted before the change in state */
> > > +     wmb();
> >
> > Not needed. set_preempt_state has the necessary barrier.
> >
> > > +
> > > +     set_preempt_state(a6xx_gpu, PREEMPT_FINISH);
> > > +
> > > +     update_wptr(gpu, a6xx_gpu->cur_ring);
> > > +
> > > +     set_preempt_state(a6xx_gpu, PREEMPT_NONE);
> > > +
> > > +     /*
> > > +      * Retrigger preemption to avoid a deadlock that might occur when preemption
> > > +      * is skipped due to it being already in flight when requested.
> > > +      */
> > > +     a6xx_preempt_trigger(gpu);
> > > +}
> > > +
> > > +void a6xx_preempt_hw_init(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     int i;
> > > +
> > > +     /* No preemption if we only have one ring */
> > > +     if (gpu->nr_rings == 1)
> > > +             return;
> > > +
> > > +     for (i = 0; i < gpu->nr_rings; i++) {
> > > +             struct a6xx_preempt_record *record_ptr =
> > > +                     a6xx_gpu->preempt[i] + PREEMPT_OFFSET_PRIV_NON_SECURE;
> > > +             record_ptr->wptr = 0;
> > > +             record_ptr->rptr = 0;
> > > +             record_ptr->rptr_addr = shadowptr(a6xx_gpu, gpu->rb[i]);
> > > +             record_ptr->info = 0;
> > > +             record_ptr->data = 0;
> > > +             record_ptr->rbase = gpu->rb[i]->iova;
> > > +     }
> > > +
> > > +     /* Write a 0 to signal that we aren't switching pagetables */
> > > +     gpu_write64(gpu, REG_A6XX_CP_CONTEXT_SWITCH_SMMU_INFO, 0);
> > > +
> > > +     /* Enable the GMEM save/restore feature for preemption */
> > > +     gpu_write(gpu, REG_A6XX_RB_CONTEXT_SWITCH_GMEM_SAVE_RESTORE, 0x1);
> > > +
> > > +     /* Reset the preemption state */
> > > +     set_preempt_state(a6xx_gpu, PREEMPT_NONE);
> > > +
> > > +     spin_lock_init(&a6xx_gpu->eval_lock);
> > > +
> > > +     /* Always come up on rb 0 */
> > > +     a6xx_gpu->cur_ring = gpu->rb[0];
> > > +}
> > > +
> > > +void a6xx_preempt_trigger(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     u64 preempt_offset_priv_secure;
> > > +     unsigned long flags;
> > > +     struct msm_ringbuffer *ring;
> > > +     unsigned int cntl;
> > > +
> > > +     if (gpu->nr_rings == 1)
> > > +             return;
> > > +
> > > +     /*
> > > +      * Lock to make sure another thread attempting preemption doesn't skip it
> > > +      * while we are still evaluating the next ring. This makes sure the other
> > > +      * thread does start preemption if we abort it and avoids a soft lock.
> > > +      */
> > > +     spin_lock_irqsave(&a6xx_gpu->eval_lock, flags);
> > > +
> > > +     /*
> > > +      * Try to start preemption by moving from NONE to START. If
> > > +      * unsuccessful, a preemption is already in flight
> > > +      */
> > > +     if (!try_preempt_state(a6xx_gpu, PREEMPT_NONE, PREEMPT_START)) {
> > > +             spin_unlock_irqrestore(&a6xx_gpu->eval_lock, flags);
> > > +             return;
> > > +     }
> > > +
> > > +     cntl = A6XX_CP_CONTEXT_SWITCH_CNTL_LEVEL(a6xx_gpu->preempt_level);
> > > +
> > > +     if (a6xx_gpu->skip_save_restore)
> > > +             cntl |= A6XX_CP_CONTEXT_SWITCH_CNTL_SKIP_SAVE_RESTORE;
> > > +
> > > +     if (a6xx_gpu->uses_gmem)
> > > +             cntl |= A6XX_CP_CONTEXT_SWITCH_CNTL_USES_GMEM;
> > > +
> > > +     cntl |= A6XX_CP_CONTEXT_SWITCH_CNTL_STOP;
> > > +
> > > +     /* Get the next ring to preempt to */
> > > +     ring = get_next_ring(gpu);
> > > +
> > > +     /*
> > > +      * If no ring is populated or the highest priority ring is the current
> > > +      * one do nothing except to update the wptr to the latest and greatest
> > > +      */
> > > +     if (!ring || (a6xx_gpu->cur_ring == ring)) {
> > > +             set_preempt_state(a6xx_gpu, PREEMPT_FINISH);
> > > +             update_wptr(gpu, a6xx_gpu->cur_ring);
> > > +             set_preempt_state(a6xx_gpu, PREEMPT_NONE);
> > > +             spin_unlock_irqrestore(&a6xx_gpu->eval_lock, flags);
> > > +             return;
> > > +     }
> > > +
> > > +     spin_unlock_irqrestore(&a6xx_gpu->eval_lock, flags);
> > > +
> > > +     spin_lock_irqsave(&ring->preempt_lock, flags);
> > > +
> > > +     struct a7xx_cp_smmu_info *smmu_info_ptr =
> > > +             a6xx_gpu->preempt[ring->id] + PREEMPT_OFFSET_SMMU_INFO;
> > > +     struct a6xx_preempt_record *record_ptr =
> > > +             a6xx_gpu->preempt[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE;
> > > +     u64 ttbr0 = ring->memptrs->ttbr0;
> > > +     u32 context_idr = ring->memptrs->context_idr;
> > > +
> > > +     smmu_info_ptr->ttbr0 = ttbr0;
> > > +     smmu_info_ptr->context_idr = context_idr;
> > > +     record_ptr->wptr = get_wptr(ring);
> > > +
> > > +     /*
> > > +      * The GPU will write the wptr we set above when we preempt. Reset
> > > +      * skip_inline_wptr to make sure that we don't write WPTR to the same
> > > +      * thing twice. It's still possible subsequent submissions will update
> > > +      * wptr again, in which case they will set the flag to true. This has
> > > +      * to be protected by the lock for setting the flag and updating wptr
> > > +      * to be atomic.
> > > +      */
> > > +     ring->skip_inline_wptr = false;
> > > +
> > > +     spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > > +
> > > +     gpu_write64(gpu,
> > > +             REG_A6XX_CP_CONTEXT_SWITCH_SMMU_INFO,
> > > +             a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_SMMU_INFO);
> > > +
> > > +     gpu_write64(gpu,
> > > +             REG_A6XX_CP_CONTEXT_SWITCH_PRIV_NON_SECURE_RESTORE_ADDR,
> > > +             a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE);
> > > +
> > > +     preempt_offset_priv_secure =
> > > +             PREEMPT_OFFSET_PRIV_SECURE(adreno_gpu->info->preempt_record_size);
> > > +     gpu_write64(gpu,
> > > +             REG_A6XX_CP_CONTEXT_SWITCH_PRIV_SECURE_RESTORE_ADDR,
> > > +             a6xx_gpu->preempt_iova[ring->id] + preempt_offset_priv_secure);
> >
> > Secure buffers are not supported currently, so we can skip this and the
> > context record allocation. Anyway this has to be a separate buffer
> > mapped in secure pagetable which don't currently have. We can skip the
> > same in pseudo register packet too.
> >
> > > +
> > > +     a6xx_gpu->next_ring = ring;
> > > +
> > > +     /* Start a timer to catch a stuck preemption */
> > > +     mod_timer(&a6xx_gpu->preempt_timer, jiffies + msecs_to_jiffies(10000));
> > > +
> > > +     /* Set the preemption state to triggered */
> > > +     set_preempt_state(a6xx_gpu, PREEMPT_TRIGGERED);
> > > +
> > > +     /* Make sure any previous writes to WPTR are posted */
> > > +     gpu_read(gpu, REG_A6XX_CP_RB_WPTR);
> > > +
> > > +     /* Make sure everything is written before hitting the button */
> > > +     wmb();
> >
> > This and the above read back looks unnecessary. All writes to gpu are
> > ordered anyway.
> 
> I thought the whole reason for
> https://lore.kernel.org/linux-kernel/20240508-topic-adreno-v1-1-1babd05c119d@linaro.org/
> is that memory-mapped writes to different GPU registers are *not*
> necessarily ordered from the GPU's perspective (even if they are from
> the CPU). That's why I suggested the readback. Or am I missing
> something?

Lets consider that GBIF unhalt sequence as an exception. Generally, we
can consider writes to gpu registers to be ordered.

-Akhil.

> 
> >
> > > +
> > > +     /* Trigger the preemption */
> > > +     gpu_write(gpu, REG_A6XX_CP_CONTEXT_SWITCH_CNTL, cntl);
> > > +}
> > > +
> > > +static int preempt_init_ring(struct a6xx_gpu *a6xx_gpu,
> > > +             struct msm_ringbuffer *ring)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = &a6xx_gpu->base;
> > > +     struct msm_gpu *gpu = &adreno_gpu->base;
> > > +     struct drm_gem_object *bo = NULL;
> > > +     phys_addr_t ttbr;
> > > +     u64 iova = 0;
> > > +     void *ptr;
> > > +     int asid;
> > > +
> > > +     ptr = msm_gem_kernel_new(gpu->dev,
> > > +             PREEMPT_SIZE(adreno_gpu->info->preempt_record_size),
> > > +             MSM_BO_WC | MSM_BO_MAP_PRIV, gpu->aspace, &bo, &iova);
> >
> > set a name?
> >
> > > +
> > > +     memset(ptr, 0, PREEMPT_SIZE(adreno_gpu->info->preempt_record_size));
> > > +
> > > +     if (IS_ERR(ptr))
> > > +             return PTR_ERR(ptr);
> > > +
> > > +     a6xx_gpu->preempt_bo[ring->id] = bo;
> > > +     a6xx_gpu->preempt_iova[ring->id] = iova;
> > > +     a6xx_gpu->preempt[ring->id] = ptr;
> > > +
> > > +     struct a7xx_cp_smmu_info *smmu_info_ptr = ptr + PREEMPT_OFFSET_SMMU_INFO;
> > > +     struct a6xx_preempt_record *record_ptr = ptr + PREEMPT_OFFSET_PRIV_NON_SECURE;
> > > +
> > > +     msm_iommu_pagetable_params(gpu->aspace->mmu, &ttbr, &asid);
> > > +
> > > +     smmu_info_ptr->magic = GEN7_CP_SMMU_INFO_MAGIC;
> > > +     smmu_info_ptr->ttbr0 = ttbr;
> > > +     smmu_info_ptr->asid = 0xdecafbad;
> > > +     smmu_info_ptr->context_idr = 0;
> > > +
> > > +     /* Set up the defaults on the preemption record */
> > > +     record_ptr->magic = A6XX_PREEMPT_RECORD_MAGIC;
> > > +     record_ptr->info = 0;
> > > +     record_ptr->data = 0;
> > > +     record_ptr->rptr = 0;
> > > +     record_ptr->wptr = 0;
> > > +     record_ptr->cntl = MSM_GPU_RB_CNTL_DEFAULT;
> > > +     record_ptr->rbase = ring->iova;
> > > +     record_ptr->counter = 0;
> > > +     record_ptr->bv_rptr_addr = rbmemptr(ring, bv_rptr);
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +void a6xx_preempt_fini(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     int i;
> > > +
> > > +     for (i = 0; i < gpu->nr_rings; i++)
> > > +             msm_gem_kernel_put(a6xx_gpu->preempt_bo[i], gpu->aspace);
> > > +}
> > > +
> > > +void a6xx_preempt_init(struct msm_gpu *gpu)
> > > +{
> > > +     struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > +     struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > > +     int i;
> > > +
> > > +     /* No preemption if we only have one ring */
> > > +     if (gpu->nr_rings <= 1)
> > > +             return;
> > > +
> > > +     for (i = 0; i < gpu->nr_rings; i++) {
> > > +             if (preempt_init_ring(a6xx_gpu, gpu->rb[i]))
> > > +                     goto fail;
> > > +     }
> > > +
> > > +     /* TODO: make this configurable? */
> > > +     a6xx_gpu->preempt_level = 1;
> > > +     a6xx_gpu->uses_gmem = 1;
> > > +     a6xx_gpu->skip_save_restore = 1;
> > > +
> > > +     timer_setup(&a6xx_gpu->preempt_timer, a6xx_preempt_timer, 0);
> > > +
> > > +     return;
> > > +fail:
> >
> > Log an error so that preemption is not disabled silently?
> >
> > > +     /*
> > > +      * On any failure our adventure is over. Clean up and
> > > +      * set nr_rings to 1 to force preemption off
> > > +      */
> > > +     a6xx_preempt_fini(gpu);
> > > +     gpu->nr_rings = 1;
> > > +
> > > +     return;
> > > +}
> > > diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.h b/drivers/gpu/drm/msm/msm_ringbuffer.h
> > > index 40791b2ade46..7dde6a312511 100644
> > > --- a/drivers/gpu/drm/msm/msm_ringbuffer.h
> > > +++ b/drivers/gpu/drm/msm/msm_ringbuffer.h
> > > @@ -36,6 +36,7 @@ struct msm_rbmemptrs {
> > >
> > >       volatile struct msm_gpu_submit_stats stats[MSM_GPU_SUBMIT_STATS_COUNT];
> > >       volatile u64 ttbr0;
> > > +     volatile u32 context_idr;
> > >  };
> > >
> > >  struct msm_cp_state {
> > > @@ -100,6 +101,12 @@ struct msm_ringbuffer {
> > >        * preemption.  Can be aquired from irq context.
> > >        */
> > >       spinlock_t preempt_lock;
> > > +
> > > +     /*
> > > +      * Whether we skipped writing wptr and it needs to be updated in the
> > > +      * future when the ring becomes current.
> > > +      */
> > > +     bool skip_inline_wptr;
> >
> > nit: does 'restore_wptr' makes more sense? Or something better?  Basically, name it based
> > on the future action?
> >
> > -Akhil
> >
> > >  };
> > >
> > >  struct msm_ringbuffer *msm_ringbuffer_new(struct msm_gpu *gpu, int id,
> > >
> > > --
> > > 2.46.0
> > >

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