linux-kernel - Re: [PATCH] drm/msm/dpu: protect ctl ops calls with validity checks

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Date: Thu, 20 Jun 2024 09:41:59 -0700
From: Rob Clark <robdclark@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Abhinav Kumar <quic_abhinavk@...cinc.com>, freedreno@...ts.freedesktop.org, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org, 
	quic_jesszhan@...cinc.com, dan.carpenter@...aro.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dpu: protect ctl ops calls with validity checks

On Thu, Jun 20, 2024 at 6:08 AM Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On Thu, 20 Jun 2024 at 00:27, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
> >
> > dpu_encoder_helper_phys_cleanup() calls the ctl ops without checking if
> > the ops are assigned causing discrepancy between its callers where the
> > checks are performed and the API itself which does not.
> >
> > Two approaches can be taken: either drop the checks even in the caller
> > OR add the checks even in dpu_encoder_helper_phys_cleanup().
> >
> > Adopt the latter approach as ctl ops are assigned revision based so may not
> > be always assigned.
>
> NAK, these calls are always assigned. Please make sure that they are
> documented as required and drop offending checks.

agreed, I'd rather see the obvious crash if somehow a required
callback didn't get set up, than a subtle/silent problem.  It is
easier to debug that way.

BR,
-R

> >
> > Fixes: d7d0e73f7de3 ("drm/msm/dpu: introduce the dpu_encoder_phys_* for writeback")
> > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > Closes: https://lore.kernel.org/all/464fbd84-0d1c-43c3-a40b-31656ac06456@moroto.mountain/T/
> > Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > index 708657598cce..7f7e6d4e974b 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > @@ -2180,9 +2180,12 @@ void dpu_encoder_helper_phys_cleanup(struct dpu_encoder_phys *phys_enc)
> >         if (ctl->ops.reset_intf_cfg)
> >                 ctl->ops.reset_intf_cfg(ctl, &intf_cfg);
> >
> > -       ctl->ops.trigger_flush(ctl);
> > -       ctl->ops.trigger_start(ctl);
> > -       ctl->ops.clear_pending_flush(ctl);
> > +       if (ctl->ops.trigger_flush)
> > +               ctl->ops.trigger_flush(ctl);
> > +       if (ctl->ops.trigger_start)
> > +               ctl->ops.trigger_start(ctl);
> > +       if (ctl->ops.clear_pending_flush)
> > +               ctl->ops.clear_pending_flush(ctl);
> >  }
> >
> >  void dpu_encoder_helper_phys_setup_cdm(struct dpu_encoder_phys *phys_enc,
> > --
> > 2.44.0
> >
>
>
> --
> With best wishes
> Dmitry