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Message-ID: <gyskd3jye43w4flhngmnelf7zaajrcqxual4ylsy5ql4xwlacd@ndzdqx77gqsj>
Date: Wed, 8 Jan 2025 04:09:17 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] drm/msm/dpu: rate limit snapshot capture for mmu
 faults

On Tue, Jan 07, 2025 at 05:34:20PM -0800, Abhinav Kumar wrote:
> 
> 
> On 12/18/2024 1:33 PM, Jessica Zhang wrote:
> > 
> > 
> > On 12/18/2024 3:20 AM, Dmitry Baryshkov wrote:
> > > On Tue, Dec 17, 2024 at 04:27:57PM -0800, Jessica Zhang wrote:
> > > > From: Abhinav Kumar <quic_abhinavk@...cinc.com>
> > > > 
> > > > There is no recovery mechanism in place yet to recover from mmu
> > > > faults for DPU. We can only prevent the faults by making sure there
> > > > is no misconfiguration.
> > > > 
> > > > Rate-limit the snapshot capture for mmu faults to once per
> > > > msm_atomic_commit_tail() as that should be sufficient to capture
> > > > the snapshot for debugging otherwise there will be a lot of DPU
> > > > snapshots getting captured for the same fault which is redundant
> > > > and also might affect capturing even one snapshot accurately.
> > > > 
> > > > Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> > > > Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> > > > ---
> > > >   drivers/gpu/drm/msm/msm_atomic.c | 2 ++
> > > >   drivers/gpu/drm/msm/msm_kms.c    | 5 ++++-
> > > >   drivers/gpu/drm/msm/msm_kms.h    | 3 +++
> > > >   3 files changed, 9 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/msm/msm_atomic.c
> > > > b/drivers/gpu/drm/msm/msm_atomic.c
> > > > index 9c45d641b5212c11078ab38c13a519663d85e10a..9ad7eeb14d4336abd9d8a8eb1382bdddce80508a
> > > > 100644
> > > > --- a/drivers/gpu/drm/msm/msm_atomic.c
> > > > +++ b/drivers/gpu/drm/msm/msm_atomic.c
> > > > @@ -228,6 +228,8 @@ void msm_atomic_commit_tail(struct
> > > > drm_atomic_state *state)
> > > >       if (kms->funcs->prepare_commit)
> > > >           kms->funcs->prepare_commit(kms, state);
> > > > +    kms->fault_snapshot_capture = 0;
> > > > +
> > > 
> > > - Please move it before the prepare_commit().
> > > - You are accessing the same variable from different threads / cores.
> > >    There should be some kind of a sync barrier.
> > 
> > Hi Dmitry,
> > 
> > Ack, will add a lock for the snapshot capture counter.
> > 
> > Thanks,
> > 
> > Jessica Zhang
> > 
> 
> We cannot have a mutex lock because msm_kms_fault_handler cannot hold a
> mutex. So we need an atomic variable in this case.

Or a spinlock.

> 
> > > 
> > > >       /*
> > > >        * Push atomic updates down to hardware:
> > > >        */
> > > > diff --git a/drivers/gpu/drm/msm/msm_kms.c
> > > > b/drivers/gpu/drm/msm/msm_kms.c
> > > > index 78830e446355f77154fa21a5d107635bc88ba3ed..3327caf396d4fc905dc127f09515559c12666dc8
> > > > 100644
> > > > --- a/drivers/gpu/drm/msm/msm_kms.c
> > > > +++ b/drivers/gpu/drm/msm/msm_kms.c
> > > > @@ -168,7 +168,10 @@ static int msm_kms_fault_handler(void *arg,
> > > > unsigned long iova, int flags, void
> > > >   {
> > > >       struct msm_kms *kms = arg;
> > > > -    msm_disp_snapshot_state(kms->dev);
> > > > +    if (!kms->fault_snapshot_capture) {
> > > > +        msm_disp_snapshot_state(kms->dev);
> > > > +        kms->fault_snapshot_capture++;
> > > > +    }
> > > >       return -ENOSYS;
> > > >   }
> > > > diff --git a/drivers/gpu/drm/msm/msm_kms.h
> > > > b/drivers/gpu/drm/msm/msm_kms.h
> > > > index e60162744c669773b6e5aef824a173647626ab4e..3ac089e26e14b824567f3cd2c62f82a1b9ea9878
> > > > 100644
> > > > --- a/drivers/gpu/drm/msm/msm_kms.h
> > > > +++ b/drivers/gpu/drm/msm/msm_kms.h
> > > > @@ -128,6 +128,9 @@ struct msm_kms {
> > > >       int irq;
> > > >       bool irq_requested;
> > > > +    /* rate limit the snapshot capture to once per attach */
> > > > +    int fault_snapshot_capture;
> > > > +
> > > >       /* mapper-id used to request GEM buffer mapped for scanout: */
> > > >       struct msm_gem_address_space *aspace;
> > > > 
> > > > -- 
> > > > 2.34.1
> > > > 
> > > 
> > > -- 
> > > With best wishes
> > > Dmitry
> > 

-- 
With best wishes
Dmitry

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