Date:   Fri, 10 Jun 2022 08:06:26 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Chia-I Wu <olvaffe@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Eric Anholt <eric@...olt.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        Sean Paul <sean@...rly.run>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        Yangtao Li <tiny.windzz@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] drm/msm: Avoid unclocked GMU register access in 6xx gpu_busy

On Thu, Jun 9, 2022 at 5:10 PM Douglas Anderson <dianders@...omium.org> wrote:
>
> From testing on sc7180-trogdor devices, reading the GMU registers
> needs the GMU clocks to be enabled. Those clocks get turned on in
> a6xx_gmu_resume(). Confusingly enough, that function is called as a
> result of the runtime_pm of the GPU "struct device", not the GMU
> "struct device". Unfortunately the current a6xx_gpu_busy() grabs a
> reference to the GMU's "struct device".
>
> The fact that we were grabbing the wrong reference was easily seen to
> cause crashes that happen if we change the GPU's pm_runtime usage to
> not use autosuspend. It's also believed to cause some long tail GPU
> crashes even with autosuspend.
>
> We could look at changing it so that we do pm_runtime_get_if_in_use()
> on the GPU's "struct device", but then we run into a different
> problem. pm_runtime_get_if_in_use() will return 0 for the GPU's
> "struct device" the whole time when we're in the "autosuspend
> delay". That is, when we drop the last reference to the GPU but we're
> waiting a period before actually suspending then we'll think the GPU
> is off. One reason that's bad is that if the GPU didn't actually turn
> off then the cycle counter doesn't lose state and that throws off all
> of our calculations.
>
> Let's change the code to keep track of the suspend state of
> devfreq. msm_devfreq_suspend() is always called before we actually
> suspend the GPU and msm_devfreq_resume() after we resume it. This
> means we can use the suspended state to know if we're powered or not.
>
> NOTE: one might wonder when exactly our status function is called when
> devfreq is supposed to be disabled. The stack crawl I captured was:
>   msm_devfreq_get_dev_status
>   devfreq_simple_ondemand_func
>   devfreq_update_target
>   qos_notifier_call
>   qos_max_notifier_call
>   blocking_notifier_call_chain
>   pm_qos_update_target
>   freq_qos_apply
>   apply_constraint
>   __dev_pm_qos_update_request
>   dev_pm_qos_update_request
>   msm_devfreq_idle_work
>
> Fixes: eadf79286a4b ("drm/msm: Check for powered down HW in the devfreq callbacks")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
> Changes in v3:
> - Totally rewrote to not use the pm_runtime functions.
> - Moved the code to be common for all adreno GPUs.
>
> Changes in v2:
> - Move the set_freq runtime pm grab to the GPU file.
> - Use <= for the pm_runtime test, not ==.
>
>  drivers/gpu/drm/msm/adreno/a5xx_gpu.c |  8 ------
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 13 ++++-----
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 12 +++------
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.h |  3 ++-
>  drivers/gpu/drm/msm/msm_gpu.h         |  9 ++++++-
>  drivers/gpu/drm/msm/msm_gpu_devfreq.c | 39 +++++++++++++++++++++------
>  6 files changed, 51 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> index c424e9a37669..3dcec7acb384 100644
> --- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> @@ -1666,18 +1666,10 @@ static u64 a5xx_gpu_busy(struct msm_gpu *gpu, unsigned long *out_sample_rate)
>  {
>         u64 busy_cycles;
>
> -       /* Only read the gpu busy if the hardware is already active */
> -       if (pm_runtime_get_if_in_use(&gpu->pdev->dev) == 0) {
> -               *out_sample_rate = 1;
> -               return 0;
> -       }
> -
>         busy_cycles = gpu_read64(gpu, REG_A5XX_RBBM_PERFCTR_RBBM_0_LO,
>                         REG_A5XX_RBBM_PERFCTR_RBBM_0_HI);
>         *out_sample_rate = clk_get_rate(gpu->core_clk);
>
> -       pm_runtime_put(&gpu->pdev->dev);
> -
>         return busy_cycles;
>  }
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index 9f76f5b15759..dc715d88ff21 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> @@ -102,7 +102,8 @@ bool a6xx_gmu_gx_is_on(struct a6xx_gmu *gmu)
>                 A6XX_GMU_SPTPRAC_PWR_CLK_STATUS_GX_HM_CLK_OFF));
>  }
>
> -void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
> +void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp,
> +                      bool suspended)
>  {
>         struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>         struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> @@ -127,15 +128,16 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
>
>         /*
>          * This can get called from devfreq while the hardware is idle. Don't
> -        * bring up the power if it isn't already active
> +        * bring up the power if it isn't already active. All we're doing here
> +        * is updating the frequency so that when we come back online we're at
> +        * the right rate.
>          */
> -       if (pm_runtime_get_if_in_use(gmu->dev) == 0)
> +       if (suspended)
>                 return;
>
>         if (!gmu->legacy) {
>                 a6xx_hfi_set_freq(gmu, perf_index);
>                 dev_pm_opp_set_opp(&gpu->pdev->dev, opp);
> -               pm_runtime_put(gmu->dev);
>                 return;
>         }
>
> @@ -159,7 +161,6 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
>                 dev_err(gmu->dev, "GMU set GPU frequency error: %d\n", ret);
>
>         dev_pm_opp_set_opp(&gpu->pdev->dev, opp);
> -       pm_runtime_put(gmu->dev);
>  }
>
>  unsigned long a6xx_gmu_get_freq(struct msm_gpu *gpu)
> @@ -895,7 +896,7 @@ static void a6xx_gmu_set_initial_freq(struct msm_gpu *gpu, struct a6xx_gmu *gmu)
>                 return;
>
>         gmu->freq = 0; /* so a6xx_gmu_set_freq() doesn't exit early */
> -       a6xx_gmu_set_freq(gpu, gpu_opp);
> +       a6xx_gmu_set_freq(gpu, gpu_opp, false);
>         dev_pm_opp_put(gpu_opp);
>  }
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 42ed9a3c4905..8c02a67f29f2 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1658,27 +1658,21 @@ static u64 a6xx_gpu_busy(struct msm_gpu *gpu, unsigned long *out_sample_rate)
>         /* 19.2MHz */
>         *out_sample_rate = 19200000;
>
> -       /* Only read the gpu busy if the hardware is already active */
> -       if (pm_runtime_get_if_in_use(a6xx_gpu->gmu.dev) == 0)
> -               return 0;
> -
>         busy_cycles = gmu_read64(&a6xx_gpu->gmu,
>                         REG_A6XX_GMU_CX_GMU_POWER_COUNTER_XOCLK_0_L,
>                         REG_A6XX_GMU_CX_GMU_POWER_COUNTER_XOCLK_0_H);
>
> -
> -       pm_runtime_put(a6xx_gpu->gmu.dev);
> -
>         return busy_cycles;
>  }
>
> -static void a6xx_gpu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
> +static void a6xx_gpu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp,
> +                             bool suspended)
>  {
>         struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>         struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
>
>         mutex_lock(&a6xx_gpu->gmu.lock);
> -       a6xx_gmu_set_freq(gpu, opp);
> +       a6xx_gmu_set_freq(gpu, opp, suspended);
>         mutex_unlock(&a6xx_gpu->gmu.lock);
>  }
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> index 86e0a7c3fe6d..ab853f61db63 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> @@ -77,7 +77,8 @@ void a6xx_gmu_clear_oob(struct a6xx_gmu *gmu, enum a6xx_gmu_oob_state state);
>  int a6xx_gmu_init(struct a6xx_gpu *a6xx_gpu, struct device_node *node);
>  void a6xx_gmu_remove(struct a6xx_gpu *a6xx_gpu);
>
> -void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp);
> +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);
>
>  void a6xx_show(struct msm_gpu *gpu, struct msm_gpu_state *state,
> diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
> index 6def00883046..7ced1a30d4e8 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.h
> +++ b/drivers/gpu/drm/msm/msm_gpu.h
> @@ -68,7 +68,8 @@ struct msm_gpu_funcs {
>         struct msm_gpu_state *(*gpu_state_get)(struct msm_gpu *gpu);
>         int (*gpu_state_put)(struct msm_gpu_state *state);
>         unsigned long (*gpu_get_freq)(struct msm_gpu *gpu);
> -       void (*gpu_set_freq)(struct msm_gpu *gpu, struct dev_pm_opp *opp);
> +       void (*gpu_set_freq)(struct msm_gpu *gpu, struct dev_pm_opp *opp,
> +                            bool suspended);

nit, I suppose we should add a comment that gpu_set_freq()/gpu_busy()
should *not* call runpm get/put as they are called with lock held

Otherwise looks good to me.. kinda sad that we have to track the
suspended state behind runpm's back, but I don't really see any better
way.

Reviewed-by: Rob Clark <robdclark@...il.com>

>         struct msm_gem_address_space *(*create_address_space)
>                 (struct msm_gpu *gpu, struct platform_device *pdev);
>         struct msm_gem_address_space *(*create_private_address_space)
> @@ -92,6 +93,9 @@ struct msm_gpu_devfreq {
>         /** devfreq: devfreq instance */
>         struct devfreq *devfreq;
>
> +       /** lock: lock for "suspended", "busy_cycles", and "time" */
> +       struct mutex lock;
> +
>         /**
>          * idle_constraint:
>          *
> @@ -135,6 +139,9 @@ struct msm_gpu_devfreq {
>          * elapsed
>          */
>         struct msm_hrtimer_work boost_work;
> +
> +       /** suspended: tracks if we're suspended */
> +       bool suspended;
>  };
>
>  struct msm_gpu {
> diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> index d2539ca78c29..ea94bc18e72e 100644
> --- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> +++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> @@ -20,6 +20,7 @@ static int msm_devfreq_target(struct device *dev, unsigned long *freq,
>                 u32 flags)
>  {
>         struct msm_gpu *gpu = dev_to_gpu(dev);
> +       struct msm_gpu_devfreq *df = &gpu->devfreq;
>         struct dev_pm_opp *opp;
>
>         /*
> @@ -32,10 +33,13 @@ static int msm_devfreq_target(struct device *dev, unsigned long *freq,
>
>         trace_msm_gpu_freq_change(dev_pm_opp_get_freq(opp));
>
> -       if (gpu->funcs->gpu_set_freq)
> -               gpu->funcs->gpu_set_freq(gpu, opp);
> -       else
> +       if (gpu->funcs->gpu_set_freq) {
> +               mutex_lock(&df->lock);
> +               gpu->funcs->gpu_set_freq(gpu, opp, df->suspended);
> +               mutex_unlock(&df->lock);
> +       } else {
>                 clk_set_rate(gpu->core_clk, *freq);
> +       }
>
>         dev_pm_opp_put(opp);
>
> @@ -58,15 +62,24 @@ static void get_raw_dev_status(struct msm_gpu *gpu,
>         unsigned long sample_rate;
>         ktime_t time;
>
> +       mutex_lock(&df->lock);
> +
>         status->current_frequency = get_freq(gpu);
> -       busy_cycles = gpu->funcs->gpu_busy(gpu, &sample_rate);
>         time = ktime_get();
> -
> -       busy_time = busy_cycles - df->busy_cycles;
>         status->total_time = ktime_us_delta(time, df->time);
> +       df->time = time;
>
> +       if (df->suspended) {
> +               mutex_unlock(&df->lock);
> +               status->busy_time = 0;
> +               return;
> +       }
> +
> +       busy_cycles = gpu->funcs->gpu_busy(gpu, &sample_rate);
> +       busy_time = busy_cycles - df->busy_cycles;
>         df->busy_cycles = busy_cycles;
> -       df->time = time;
> +
> +       mutex_unlock(&df->lock);
>
>         busy_time *= USEC_PER_SEC;
>         do_div(busy_time, sample_rate);
> @@ -175,6 +188,8 @@ void msm_devfreq_init(struct msm_gpu *gpu)
>         if (!gpu->funcs->gpu_busy)
>                 return;
>
> +       mutex_init(&df->lock);
> +
>         dev_pm_qos_add_request(&gpu->pdev->dev, &df->idle_freq,
>                                DEV_PM_QOS_MAX_FREQUENCY,
>                                PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
> @@ -244,12 +259,16 @@ void msm_devfreq_cleanup(struct msm_gpu *gpu)
>  void msm_devfreq_resume(struct msm_gpu *gpu)
>  {
>         struct msm_gpu_devfreq *df = &gpu->devfreq;
> +       unsigned long sample_rate;
>
>         if (!has_devfreq(gpu))
>                 return;
>
> -       df->busy_cycles = 0;
> +       mutex_lock(&df->lock);
> +       df->busy_cycles = gpu->funcs->gpu_busy(gpu, &sample_rate);
>         df->time = ktime_get();
> +       df->suspended = false;
> +       mutex_unlock(&df->lock);
>
>         devfreq_resume_device(df->devfreq);
>  }
> @@ -261,6 +280,10 @@ void msm_devfreq_suspend(struct msm_gpu *gpu)
>         if (!has_devfreq(gpu))
>                 return;
>
> +       mutex_lock(&df->lock);
> +       df->suspended = true;
> +       mutex_unlock(&df->lock);
> +
>         devfreq_suspend_device(df->devfreq);
>
>         cancel_idle_work(df);
> --
> 2.36.1.476.g0c4daa206d-goog
>

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