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

[Dario Binacchi]

Hi Jagan and Dave,

On Wed, Dec 6, 2023 at 2:57 PM Michael Nazzareno Trimarchi
<michael at amarulasolutions.com> wrote:
>
> Hi Jagan
>
> On Wed, Dec 6, 2023 at 2:31 PM Jagan Teki <jagan at amarulasolutions.com> wrote:
> >
> > Hi Dario,
> >
> > On Wed, Dec 6, 2023 at 6:57 PM Dario Binacchi
> > <dario.binacchi at amarulasolutions.com> wrote:
> > >
> > > Hi Dave and Jagan,
> > >
> > > On Tue, Dec 5, 2023 at 4:39 PM Dave Stevenson
> > > <dave.stevenson at raspberrypi.com> wrote:
> > > >
> > > > Hi Dario
> > > >
> > > > On Tue, 5 Dec 2023 at 10:54, Dario Binacchi
> > > > <dario.binacchi at 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 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.

Starting from my use case:

# cat /sys/kernel/debug/dri/32e00000.lcdif/bridge_chains
encoder[36]
bridge[0] type: 16, ops: 0x0, OF:
/soc at 0/bus at 32c00000/dsi at 32e10000:fsl,imx8mn-mipi-dsim
bridge[1] type: 16, ops: 0x8, OF:
/soc at 0/bus at 32c00000/dsi at 32e10000/panel at 0:sharp,ls068b3sx0

I developed a pass through MIPI-DSI bridge driver to try to test your case:
# cat /sys/kernel/debug/dri/32e00000.lcdif/bridge_chains
encoder[36]
bridge[0] type: 16, ops: 0x0, OF:
/soc at 0/bus at 32c00000/dsi at 32e10000:fsl,imx8mn-mipi-dsim
bridge[1] type: 16, ops: 0x0, OF: /pt_mipi_dsi1:amarula,pt-mipi-dsi
bridge[2] type: 16, ops: 0x0, OF: /pt_mipi_dsi2:amarula,pt-mipi-dsi
bridge[3] type: 16, ops: 0x0, OF: /pt_mipi_dsi3:amarula,pt-mipi-dsi
bridge[4] type: 16, ops: 0x0, OF: /pt_mipi_dsi4:amarula,pt-mipi-dsi
bridge[5] type: 16, ops: 0x0, OF: /pt_mipi_dsi5:amarula,pt-mipi-dsi
bridge[6] type: 16, ops: 0x8, OF: /pt_mipi_dsi5/panel at 0:sharp,ls068b3sx02

The pre_enable_prev_first flag is set through the
"amarula,pre_enable_prev_first" dts property I put
in my dts.
Your and my patches give the same results (result: OK) in both your
use case and mine.
But If I test my new "enlarged" use case:

- Encoder
- bridge[0] (samsung-dsim)
- bridge[1] pre_enable_prev_first
- bridge[2] pre_enable_prev_first
- bridge[3] pre_enable_prev_first
- bridge[4] pre_enable_prev_first
- bridge[5] pre_enable_prev_first
- bridge[6] pre_enable_prev_first (Panel)

the result is:
my patches: KO
your patch: OK

So, I will remove my patches from the series.

Can the driver I implemented to test the use cases (pass through
MIPI-DSI) be considered useful for testing these
bridge pipelines?
Does it make sense to send its patch?

Thanks and regards
Dario

Dario Binacchi

Senior Embedded Linux Developer

dario.binacchi at amarulasolutions.com

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