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From:   Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
Date:   Wed, 6 Dec 2023 14:57:06 +0100
Message-ID: <CAOf5uwm_YmXz0A6nuCbJh+iszwqWyQkRRKATKyWZ33YUgZmEnw@mail.gmail.com>
Subject: Re: [PATCH v4 02/10] drm/bridge: Fix a use case in the bridge disable logic
To:     Jagan Teki <jagan@amarulasolutions.com>
Cc:     Dario Binacchi <dario.binacchi@amarulasolutions.com>,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        linux-kernel@vger.kernel.org,
        Amarula patchwork <linux-amarula@amarulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@gmail.com>,
        Frieder Schrempf <frieder.schrempf@kontron.de>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Robert Foss <rfoss@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        dri-devel@lists.freedesktop.org
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Hi Jagan

On Wed, Dec 6, 2023 at 2:31=E2=80=AFPM Jagan Teki <jagan@amarulasolutions.c=
om> wrote:
>
> Hi Dario,
>
> On Wed, Dec 6, 2023 at 6:57=E2=80=AFPM Dario Binacchi
> <dario.binacchi@amarulasolutions.com> wrote:
> >
> > Hi Dave and Jagan,
> >
> > On Tue, Dec 5, 2023 at 4:39=E2=80=AFPM Dave Stevenson
> > <dave.stevenson@raspberrypi.com> wrote:
> > >
> > > Hi Dario
> > >
> > > On Tue, 5 Dec 2023 at 10:54, Dario Binacchi
> > > <dario.binacchi@amarulasolutions.com> wrote:
> > > >
> > > > The patch fixes the code for finding the next bridge with the
> > > > "pre_enable_prev_first" flag set to false. In case this condition i=
s
> > > > not verified, i. e. there is no subsequent bridge with the flag set=
 to
> > > > false, the whole bridge list is traversed, invalidating the "next"
> > > > variable.
> > > >
> > > > The use of a new iteration variable (i. e. "iter") ensures that the=
 value
> > > > of the "next" variable is not invalidated.
> > >
> > > We already have https://patchwork.freedesktop.org/patch/529288/ that
> > > has been reviewed (but not applied) to resolve this. What does this
> > > version do differently and why?
> >
> > My patches only affect drm_atomic_bridge_chain_post_disable(), whereas
> > Jagan's patch affects both
> > drm_atomic_bridge_chain_post_disable() and drm_atomic_bridge_chain_pre_=
enable().
> > I tested Jagan's patch on my system with success and I reviewed with
> > Michael Trimarchi the
> > drm_atomic_bridge_chain_pre_enable() fixing and we think it's okay.
> > We also believe that our changes to post_disable() are better, as we
> > set the 'next' variable only when required,
> > and the code is more optimized since the list_is_last() is not called
> > within the loop.
> > Would it be possible to use Jagan's patch for fixing
> > drm_atomic_bridge_chain_pre_enable() and mine for
> > fixing drm_atomic_bridge_chain_post_disable()?
> >
>
> Can you please share the post-disabled bridge chain list with the
> below example before and after your change?

We have already git commit the description in how the patch affects
the post_disable. As Dario
reported your patch is ok even in our use case. We don't have a real
use case as the one you describe.

Can we know how you test it in this use case here? Can you test our
patches of post_disable?

Thanks
Michael

>
> Example:
> - Panel
> - Bridge 1
> - Bridge 2 pre_enable_prev_first
> - Bridge 3
> - Bridge 4 pre_enable_prev_first
> - Bridge 5 pre_enable_prev_first
> - Bridge 6
> - Encoder
>
> Thanks,
> Jagan.