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

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Hi Jagan

On Wed, Dec 6, 2023 at 2:31 PM Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hi Dario,
>
> On Wed, Dec 6, 2023 at 6:57 PM Dario Binacchi
> <dario.binacchi@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hi Dave and Jagan,
> >
> > On Tue, Dec 5, 2023 at 4:39 PM Dave Stevenson
> > <dave.stevenson@xxxxxxxxxxxxxxx> wrote:
> > >
> > > Hi Dario
> > >
> > > On Tue, 5 Dec 2023 at 10:54, Dario Binacchi
> > > <dario.binacchi@xxxxxxxxxxxxxxxxxxxx> 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?

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.




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