linux-kernel - Re: [PATCH 1/4] drm/msm/a5xx: disable preemption in submits by default

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Message-ID: <20240801123823.geauowjux6r2ao72@hu-akhilpo-hyd.qualcomm.com>
Date: Thu, 1 Aug 2024 18:08:23 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Rob Clark <robdclark@...il.com>
CC: Vladimir Lypak <vladimir.lypak@...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>,
        Jordan Crouse
	<jordan@...micpenguin.net>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] drm/msm/a5xx: disable preemption in submits by
 default

On Mon, Jul 15, 2024 at 02:00:10PM -0700, Rob Clark wrote:
> On Thu, Jul 11, 2024 at 3:02 AM Vladimir Lypak <vladimir.lypak@...il.com> wrote:
> >
> > Fine grain preemption (switching from/to points within submits)
> > requires extra handling in command stream of those submits, especially
> > when rendering with tiling (using GMEM). However this handling is
> > missing at this point in mesa (and always was). For this reason we get
> > random GPU faults and hangs if more than one priority level is used
> > because local preemption is enabled prior to executing command stream
> > from submit.
> > With that said it was ahead of time to enable local preemption by
> > default considering the fact that even on downstream kernel it is only
> > enabled if requested via UAPI.
> >
> > Fixes: a7a4c19c36de ("drm/msm/a5xx: fix setting of the CP_PREEMPT_ENABLE_LOCAL register")
> > Signed-off-by: Vladimir Lypak <vladimir.lypak@...il.com>
> > ---
> >  drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> > index c0b5373e90d7..6c80d3003966 100644
> > --- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> > @@ -150,9 +150,13 @@ static void a5xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> >         OUT_PKT7(ring, CP_SET_PROTECTED_MODE, 1);
> >         OUT_RING(ring, 1);
> >
> > -       /* Enable local preemption for finegrain preemption */
> > +       /*
> > +        * Disable local preemption by default because it requires
> > +        * user-space to be aware of it and provide additional handling
> > +        * to restore rendering state or do various flushes on switch.
> > +        */
> >         OUT_PKT7(ring, CP_PREEMPT_ENABLE_LOCAL, 1);
> > -       OUT_RING(ring, 0x1);
> > +       OUT_RING(ring, 0x0);
> 
> From a quick look at the a530 pfp fw, it looks like
> CP_PREEMPT_ENABLE_LOCAL is allowed in IB1/IB2 (ie. not restricted to
> kernel RB).  So we should just disable it in the kernel, and let
> userspace send a CP_PREEMPT_ENABLE_LOCAL to enable local preemption.

Ack. AFAIU about a5x preemption, this should work.

-Akhil

> 
> BR,
> -R
> 
> >         /* Allow CP_CONTEXT_SWITCH_YIELD packets in the IB2 */
> >         OUT_PKT7(ring, CP_YIELD_ENABLE, 1);
> > --
> > 2.45.2
> >