Re: [PATCH] drm/mediatek: mtk_dsi: enable hs clock during pre-enable

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

On 7/7/26 10:51, Thorsten Leemhuis wrote:
> On 7/7/26 04:20, CK Hu (胡俊光) wrote:
>> On Mon, 2026-07-06 at 12:16 +0200, Thorsten Leemhuis wrote:
>>> On 6/22/26 15:23, Adam Thiede wrote:
>>>> On 6/22/26 06:22, Gary Bisson wrote:
>>>>> On Thu, Jun 18, 2026 at 04:06:28PM -0500, Adam Thiede wrote:
>>>>>> On 1/20/26 05:36, Gary Bisson wrote:
>>>>>>> Some bridges, such as the TI SN65DSI83, require the HS clock to be
>>>>>>> running in order to lock its PLL during its own pre-enable function.
>>>>>>>
>>>>>>> Without this change, the bridge gives the following error:
>>>>>>> sn65dsi83 14-002c: failed to lock PLL, ret=-110
>>>>>>> sn65dsi83 14-002c: Unexpected link status 0x01
>>>>>>> sn65dsi83 14-002c: reset the pipe
>>>>>>> [...]
>>>>>>
>>>>>> This commit was part of 7.1 and caused a problem for me.
>>>>>> I'm running postmarketOS (basically Alpine Linux) on a Lenovo C330
>>>>>> chromebook with a Mediatek MT8173 processor.
>>>>>> The problem: when the display on my laptop powers off (via suspend or
>>>>>> idle,
>>>>>> like xset dpms off) the picture does not come back when the display
>>>>>> powers
>>>>>> back on (from resume). The display backlight comes on and brightness is
>>>>>> adjustable but there is no picture. The only fix is to reboot.
>>>>>>
>>>>>> Reverting this commit and applying it as a patch on top of 7.1
>>>>>> addresses the
>>>>>> issue for me.
>>>>>>
>>>>>> You can view the config I'm using here:
>>>>>> https://urldefense.com/v3/__https://gitlab.postmarketos.org/postmarketOS/pmaports/-/__;!!CTRNKA9wMg0ARbw!jrsPDtSEUdaINzLlq92Li8gmsEBkTOxZ6WUzNHjvIN6CyOJjHiHkNSOhIRPXFTLPlaYlxU2uvryVkwjUAN9bmax5$
>>>>>> merge_requests/8819
>>>>>>
>>>>>> Is there any sort of testing or other debugging info I can provide to
>>>>>> help
>>>>>> address this issue?
>>>>>
>>>>> Thanks for reporting the issue, could you share some logs? Is the driver
>>>>> saying anything during resume? Also, what type of panel is used on that
>>>>> chromebook?
>>>>
>>>> The curious thing is that there are no real logs in dmesg or /var/log/
>>>> messages about this. This picture just fails to come back. If there are
>>>> some kernel params I can set to get deeper logging, that would help, but
>>>> I'm not aware of any.
>>>>
>>>> I think the panel is a "BOE NV116WHM-T00" - I used this command to get
>>>> info: cat /sys/class/drm/card0-eDP-1/edid | edid-decode
>>>>
>>>> Output: https://urldefense.com/v3/__https://termbin.com/8nbd__;!!CTRNKA9wMg0ARbw!jrsPDtSEUdaINzLlq92Li8gmsEBkTOxZ6WUzNHjvIN6CyOJjHiHkNSOhIRPXFTLPlaYlxU2uvryVkwjUAJooSyqL$
>>>
>>> This looked stalled. If I'm mistaken here, please let me known; but if
>>> no solution is in sight, should we maybe just revert the change until a
>>> proper was found?
>>
>> It's welcome anyone to provide a revert patch,
>> but I would still wait for the fixup patch until 7.2-rc4.
>> If no fixup patch exist, then apply the revert patch.
>  From my understanding of things the position in the devel cycle doesn't
> matter much in a case like this. To quote Linus statements from
> https://www.kernel.org/doc/html/latest/process/handling-regressions.html#on-how-quickly-regressions-should-be-fixed
> 
> """
>  From 2026-01-22:
> 
>   But a user complaining should basically result in an immediate fix -
>   possibly a "revert and rethink".
> 
> With a later clarification on 2026-01-28:
> 
>   It's also worth noting that "immediate" obviously doesn't mean "right
>   this *second* when the problem has been reported".
> 
>   But if it's a regression with a known commit that caused it, I think
>   the rule of thumb should generally be "within a week", preferably
>   before the next rc.
> """
> 
> Adam reported the problem about three weeks ago, so we are way past the
> "rule of thumb" timeframe Linus set.
> 
> Ciao, Thorsten

This is a kind of odd situation here. The fix from Adam is actually correct, as in,
the SN65DSI83 bridge gets broken without...

....but then, there's some more oddness going on: I tried to reproduce this on my
MT8173 Elm device, but there I can resume the system just fine, and the display is
up and running like normal?

I'm not sure what to advice here at this point - just adding some info.

Cheers,
Angelo