Re: [PATCH] drm/bridge: adv7511: Do not merge adv7511_mode_set() with atomic_enable()

[Maxime Ripard <mripard@kernel.org>]

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On Mon, May 26, 2025 at 01:19:23PM +0200, Tommaso Merciai wrote:
> Hi Laurent,
> Thanks for your comment.
> 
> On 26/05/25 12:49, Laurent Pinchart wrote:
> > On Mon, May 26, 2025 at 11:58:37AM +0200, Tommaso Merciai wrote:
> > > Hi Maxime,
> > > Thanks for your comment.
> > > 
> > > On 26/05/25 11:26, Maxime Ripard wrote:
> > > > Hi,
> > > > 
> > > > On Mon, May 26, 2025 at 10:54:52AM +0200, Tommaso Merciai wrote:
> > > > > After adv7511_mode_set() was merged into .atomic_enable(), only the
> > > > > native resolution is working when using modetest.
> > > > > 
> > > > > This is caused by incorrect timings: adv7511_mode_set() must not be
> > > > > merged into .atomic_enable().
> > > > > 
> > > > > Move adv7511_mode_set() back to the .mode_set() callback in
> > > > > drm_bridge_funcs to restore correct behavior.
> > > > > 
> > > > > Fixes: 0a9e2f0a6466 ("drm/bridge: adv7511: switch to the HDMI connector helpers")
> > > > > Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > > > Closes: https://lore.kernel.org/all/aDB8bD6cF7qiSpKd@tom-desktop/
> > > > > Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
> > > > 
> > > > Explaining why, both in the commit log and the comments, would be nice.
> > > > Because I can't think of any good reason it just can't work for that
> > > > bridge.
> > > 
> > > Sorry, let me clarify and share with you some details:
> > > 
> > > adv7511_mode_set:
> > >    - Is setting up timings registers for the DSI2HDMI bridge in our case
> > >      we are using ADV7535 bridge.
> > > 
> > > rzg2l_mipi_dsi_atomic_enable:
> > >    - Is setting up the vclock for the DSI ip
> > > 
> > > Testing new/old implementation a bit we found the following:
> > > 
> > > root@smarc-rzg3e:~# modetest -M rzg2l-du -d -s HDMI-A-1:800x600-56.25@XR24
> > > setting mode 800x600-56.25Hz on connectors HDMI-A-1, crtc 62
> > > [   49.273134] adv7511_mode_set_old: drm_mode_vrefresh(mode) = 56
> > > [   49.281006] rzg2l_mipi_dsi_atomic_enable: mode->clock: 36000
> > > 
> > > root@smarc-rzg3e:~# modetest -M rzg2l-du -d -s HDMI-A-1:800x600-56.25@XR24
> > > setting mode 800x600-56.25Hz on connectors HDMI-A-1, crtc 62
> > > [   74.076881] rzg2l_mipi_dsi_atomic_enable: mode->clock: 36000
> > > [   74.092130] adv7511_mode_set: drm_mode_vrefresh(adj_mode) = 56
> > > 
> > > Same result but different timing (in function call perspective):
> > > 
> > >    - old: adv7511_mode_set() is call before rzg2l_mipi_dsi_atomic_enable()
> > >    - new: adv7511_mode_set() is call after rzg2l_mipi_dsi_atomic_enable()
> > 
> > What is "old" and "new" here ? Is it before and after Dmitry's patch, or
> > before and after yours ? Please be precise when describing problems.
> 
> Sorry, you are completely right:
> 
>  - old --> before Dmitry's patch
>  - new --> after Dmitry's patch
> 
> > 
> > > What do you think? Thanks in advance.
> > 
> > You're only explaining above what the "old" and "new" behaviours are,
> > and claiming one of them is causing an issue, but you're not explaining
> > *why* it causes an issue. That's what your commit message is expected to
> > detail.
> > 
> 
> Thanks for the clarification! :)
> I will send v2 explaining better this.

In particular, if the driver needs to have mode_set called before
atomic_enable, you should say why moving the call to mode_set earlier in
the function wouldn't work.

Maxime

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