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

[Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>]

On 26/05/25 16:02, Tommaso Merciai wrote:
> Hi All,
> Thanks for your comments.
> 
> On 26/05/25 15:18, Dmitry Baryshkov wrote:
>> 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@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.
>>
>> 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.
>>
> 
> Some updates on my side:
> 
> I'm not seeing any differences from a regs perspective when using the 
> old driver version (before Dmitry's patch) and the new driver version 
> (after Dmitry's patch).
> 
> In particular, i2cdump -f -y 7 0x4c shows me the same result.

Please ignore this (wrong address)

The right test is: i2cdump -f -y 7 0x3d

And I'm seeing the following differences:

# WORK:
reg | val
0x3d → 0x00
0x3e → 0x00

# DON't WORK
reg | val
0x3d → 0x10
0x3e → 0x40

Thanks & Regards,
Tommaso


> 
> Unfortunately, since I don't have the ADV7535 datasheet, I believe this 
> issue may be related to the functions call sequence.
> 
> I agree with Dmitry's theory.
> 
> Let me gently know if you need some more test on my side. Thanks in 
> advance.
> 
> Regards,
> Tommaso
> 
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