linux-kernel - Re: [PATCH] drm/bridge: adv7511: Do not merge adv7511_mode_set() with atomic

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Message-ID: <7603c3b1-edff-4c02-a4a5-1d5f72720cad@oss.qualcomm.com>
Date: Mon, 26 May 2025 16:18:31 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Maxime Ripard <mripard@...nel.org>,
        Tommaso Merciai <tommaso.merciai.xr@...renesas.com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        tomm.merciai@...il.com, linux-renesas-soc@...r.kernel.org,
        biju.das.jz@...renesas.com, Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Douglas Anderson <dianders@...omium.org>,
        Adam Ford <aford173@...il.com>, Jesse Van Gavere <jesseevg@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: adv7511: Do not merge adv7511_mode_set() with
 atomic_enable()

On 26/05/2025 14:40, Maxime Ripard wrote:
> 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@...renesas.com>
>>>>>> Closes: https://lore.kernel.org/all/aDB8bD6cF7qiSpKd@tom-desktop/
>>>>>> Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@...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@...rc-rzg3e:~# modetest -M rzg2l-du -d -s HDMI-A-1:800x600-56.25@...4
>>>> 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@...rc-rzg3e:~# modetest -M rzg2l-du -d -s HDMI-A-1:800x600-56.25@...4
>>>> 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.

It might be the same thing as we had on PS8640: it had to be brought up 
before the host starts the DSI link, so that there is no clock input on 
the DSI clock lane.

-- 
With best wishes
Dmitry