linux-kernel - Re: [PATCH v4 02/10] drm/bridge: Fix a use case in the bridge disable logic

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Date:   Wed, 6 Dec 2023 19:01:10 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 02/10] drm/bridge: Fix a use case in the bridge disable logic

Hi Dario,

On Wed, Dec 6, 2023 at 6:57 PM Dario Binacchi
<dario.binacchi@...rulasolutions.com> wrote:
>
> Hi Dave and Jagan,
>
> On Tue, Dec 5, 2023 at 4:39 PM Dave Stevenson
> <dave.stevenson@...pberrypi.com> wrote:
> >
> > Hi Dario
> >
> > On Tue, 5 Dec 2023 at 10:54, Dario Binacchi
> > <dario.binacchi@...rulasolutions.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 is
> > > 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?

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.