Re: [PATCH v2 0/2] drm: bridge: ti-sn65dsi83: Improve dual-link LVDS support

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

Hello Sudarshan,

On Wed Mar 18, 2026 at 6:45 AM CET, tessolveupstream wrote:
>>>> You might want to look at recently posted:
>>>>
>>>> [PATCH 2/3] drm/bridge: ti-sn65dsi83: halve horizontal syncs for dual LVDS output
>>>
>>> Thanks for pointing this out.
>>> I tried applying the patch “[PATCH 2/3] drm/bridge: ti-sn65dsi83: halve horizontal syncs for dual LVDS output” on top of the current tree and
>>> removed the changes that I had previously added in the driver.
>>> However, with this patch applied, I am currently seeing only the backlight turning on and no image on the LVDS panel.
>>> For reference, the LVDS panel used on our platform is G133HAN01.1 and the
>>> DSI-to-dual-link LVDS bridge is SN65DSI84ZXHR.
>>
>> Thanks for having tried.
>>
>> Can you please test with both the fixes in the series applied + the test
>> pattern feature and report the results you get with and without test
>> pattern enabled?
>>
>> The patches to apply are:
>>
>>  - https://lore.kernel.org/all/20260226-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v1-1-2e15f5a9a6a0@bootlin.com/
>>  - https://lore.kernel.org/all/20260226-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v1-2-2e15f5a9a6a0@bootlin.com/
>>  - https://lore.kernel.org/lkml/20260309-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v2-1-e6aaa7e1d181@bootlin.com/
>>
>
> Thanks for the suggestions.
>
> I tested the three patches together as mentioned, but the LVDS panel
> still only shows the backlight and no image. I also tried removing the
> test-pattern patch and retesting with only the remaining two fixes, but
> the result remained the same — only the backlight turns on and no image
> is displayed.

Sure, the test pattern patch does not change anything, unless you enable
the test pattern.

>> The first thing I suggest doing on your side is testing with the 3 patches
>> mentioned above.
>>
>> If you display works, good! Let us know (you can also add your Tested-by /
>> Reviewed-by tags to the test_pattern patch too if applicable).
>>
>> If it doesn't work, compare the individual register values to find the
>> differences, try to figure out why the working setting works and how to
>> apply that change to the driver in away that keeps other boards
>> working. You're welcome to come back here to discuss it in case you can't
>> find out on your own.
>>
>
> I tested the three patches as suggested, but the panel still shows only the
> backlight with no visible image. I’m unsure how to translate the working
> register values into a generic fix based on display timings. Any guidance
> on the right direction would be helpful.

What you should do is:

 1. with your patches, and while the display is enabled (and working) do

     cat /sys/kernel/debug/regmap/4-002c/registers >regs.working

 2. remove your patches, add the 3 I mentioned, and while the display is
    enabled (but only backlight is working) do

     cat /sys/kernel/debug/regmap/4-002c/registers >regs.broken

Then compare regs.working and regs.broken. Which registers differ? Can you
give a reason for the differences?

You can come back with these values here so we may discuss them.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com