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From:   Brian Starkey <Brian.Starkey@arm.com>
To:     "Lowry Li (Arm Technology China)" <Lowry.Li@arm.com>,
        Liviu Dudau <Liviu.Dudau@arm.com>,
        "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>,
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        <maarten.lankhorst@linux.intel.com>,
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        "airlied@linux.ie" <airlied@linux.ie>,
        Ayan Halder <Ayan.Halder@arm.com>,
        "Jonathan Chai (Arm Technology China)" <Jonathan.Chai@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "Julien Yin (Arm Technology China)" <Julien.Yin@arm.com>,
        nd <nd@arm.com>
Subject: Re: [PATCH] drm/komeda: Skips the invalid writeback job
Thread-Topic: [PATCH] drm/komeda: Skips the invalid writeback job
Thread-Index: AQHVQ4nw7K9FV7USuUuF4ik2yHSO+qbc9HAAgAAFvAA=
Date:   Fri, 26 Jul 2019 14:44:30 +0000
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On Fri, Jul 26, 2019 at 04:23:56PM +0200, Daniel Vetter wrote:
> On Fri, Jul 26, 2019 at 08:13:00AM +0000, Lowry Li (Arm Technology China)=
 wrote:
> > Current DRM-CORE accepts the writeback_job with a empty fb, but that
> > is an invalid job for HW, so need to skip it when commit it to HW.
> >
> > Signed-off-by: Lowry Li (Arm Technology China) <lowry.li@arm.com>
>
> Hm, this sounds a bit like an oversight in core writeback code? Not sure
> how this can even happen, setting up a writeback job without an fb sounds
> a bit like a bug to me at least ...
>
> If we don't have a good reason for why other hw needs to accept this, the=
n
> imo this needs to be rejected in shared code. For consistent behaviour
> across all writeback supporting drivers.
> -Daniel

I think it's only this way to simplify the drm_writeback_set_fb()
implementation in the case where the property is set more than once in
the same commit (to something valid, and then 0).

The core could indeed handle it - drm_writeback_set_fb() would check
fb. If it's NULL and there's no writeback job, then it can just early
return. If it's NULL and there's already a writeback job then it
should drop the reference on the existing fb and free that job.

Could lead to the job getting alloc/freed multiple times if userspace
is insane, but meh.

-Brian

>
> > ---
> >  drivers/gpu/drm/arm/display/komeda/komeda_crtc.c         | 2 +-
> >  drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c | 9 ++++++++-
> >  2 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers=
/gpu/drm/arm/display/komeda/komeda_crtc.c
> > index 2fed1f6..372e99a 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > @@ -265,7 +265,7 @@ void komeda_crtc_handle_event(struct komeda_crtc *k=
crtc,
> >  komeda_pipeline_update(slave, old->state);
> >
> >  conn_st =3D wb_conn ? wb_conn->base.base.state : NULL;
> > -if (conn_st && conn_st->writeback_job)
> > +if (conn_st && conn_st->writeback_job && conn_st->writeback_job->fb)
> >  drm_writeback_queue_job(&wb_conn->base, conn_st);
> >
> >  /* step 2: notify the HW to kickoff the update */
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c b=
/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c
> > index 9787745..8e2ef63 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c
> > @@ -52,9 +52,16 @@
> >  struct komeda_data_flow_cfg dflow;
> >  int err;
> >
> > -if (!writeback_job || !writeback_job->fb)
> > +if (!writeback_job)
> >  return 0;
> >
> > +if (!writeback_job->fb) {
> > +if (writeback_job->out_fence)
> > +DRM_DEBUG_ATOMIC("Out fence required on a invalid writeback job.\n");
> > +
> > +return writeback_job->out_fence ? -EINVAL : 0;
> > +}
> > +
> >  if (!crtc_st->active) {
> >  DRM_DEBUG_ATOMIC("Cannot write the composition result out on a inactiv=
e CRTC.\n");
> >  return -EINVAL;
> > --
> > 1.9.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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