linux-kernel - Re: [PATCH v3 3/5] drm/msm: fix fb references in async update

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Date:   Fri, 31 May 2019 11:50:09 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Helen Koike <helen@...keco.de>
Cc:     Helen Koike <helen.koike@...labora.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        nicholas.kazlauskas@....com,
        "Grodzovsky, Andrey" <andrey.grodzovsky@....com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Sean Paul <seanpaul@...gle.com>, kernel@...labora.com,
        Harry Wentland <harry.wentland@....com>,
        Stéphane Marchesin <marcheu@...gle.com>,
        stable <stable@...r.kernel.org>, Sean Paul <sean@...rly.run>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Mamta Shukla <mamtashukla555@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v3 3/5] drm/msm: fix fb references in async update

On Fri, May 31, 2019 at 10:54 AM Helen Koike <helen@...keco.de> wrote:
>
> Hello,
>
> On 3/13/19 9:20 PM, Helen Koike wrote:
> > Async update callbacks are expected to set the old_fb in the new_state
> > so prepare/cleanup framebuffers are balanced.
> >
> > Cc: <stable@...r.kernel.org> # v4.14+
> > Fixes: 224a4c970987 ("drm/msm: update cursors asynchronously through atomic")
> > Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
> > Signed-off-by: Helen Koike <helen.koike@...labora.com>

Thanks, I'm not super happy about the refcnt'ing subtleness here
(mostly because it makes it harder to page in how things work on
kernel/display side after spending most of my time in userspace/mesa),
but I don't want to hold this up..

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

> >
> > ---
> > Hello,
> >
> > As mentioned in the cover letter,
> > But I couldn't test on MSM because I don't have the hardware and I would
> > appreciate if anyone could test it.
>
> I got this tested on a dragonboard 410c, no regressions where found and
> no extra warnings.
>
> These two tests where already failing for other reasons:
> flip-vs-cursor-crc-atomic
> flip-vs-cursor-crc-legacy
>
> If you want to see the full log:
>
> https://people.collabora.com/~koike/drm-fixes-results.zip
>
> Thanks
> Helen
>
> >
> > In other platforms (VC4, AMD, Rockchip), there is a hidden
> > drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
> > that is wrong, but I couldn't identify those here, not sure if it is hidden
> > somewhere else, but if tests fail this is probably the cause.
> >
> > Thanks!
> > Helen
> >
> > Changes in v3: None
> > Changes in v2:
> > - update CC stable and Fixes tag
> >
> >  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> > index be13140967b4..b854f471e9e5 100644
> > --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> > +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> > @@ -502,6 +502,8 @@ static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
> >  static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
> >                                          struct drm_plane_state *new_state)
> >  {
> > +     struct drm_framebuffer *old_fb = plane->state->fb;
> > +
> >       plane->state->src_x = new_state->src_x;
> >       plane->state->src_y = new_state->src_y;
> >       plane->state->crtc_x = new_state->crtc_x;
> > @@ -524,6 +526,8 @@ static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
> >
> >       *to_mdp5_plane_state(plane->state) =
> >               *to_mdp5_plane_state(new_state);
> > +
> > +     new_state->fb = old_fb;
> >  }
> >
> >  static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {
> >