Re: [PATCH v3 1/1] drm: bridge: ti-sn65dsi83: Fix DSI mode flags for stable LVDS output

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

Hello,

On Tue May 19, 2026 at 10:48 AM CEST, tessolveupstream wrote:
>
>
> On 24-04-2026 13:55, Luca Ceresoli wrote:
>> Hello,
>>
>> On Thu Apr 23, 2026 at 11:16 AM CEST, tessolveupstream wrote:
>>
>>>> I had reached out to TI for clarification and any related documentation
>>>> updates, but I have not received any response so far.Given this, it is
>>>> uncertain whether we will be able to obtain further details or official
>>>> confirmation from TI in the near term.
>>>>
>>>> I would appreciate your guidance on how you would prefer us to proceed
>>>> from here.
>>>
>>> I followed up with TI, and they pointed us to the relevant sections in the
>>> SN65DSI83/84/86 datasheets covering DSI video transmission specifications.
>>
>> Thanks for keeping on! I'm also trying to get info from TI, I'm keeping you
>> up to date if that will happen.
>>
>>>> https://www.ti.com/lit/ds/symlink/sn65dsi84.pdf?ts=1776924088430&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FSN65DSI84
>>>
>>> As per datasheet Section 7.4.7, the device operates in DSI video mode with
>>> fixed horizontal timing, where HBP, and HFP are explicitly defined and expected
>>> to be present as part of the video line structure. The timing description in
>>> this section assumes standard non‑burst video transmission with all horizontal
>>> blanking intervals accounted for.
>>>
>>> The datasheet does not document support for DSI video burst mode,
>>
>> This sentence seems incorrect. Section 7.4.7 starts with this sentence:
>> "The SN65DSI84 supports burst video mode and non-burst video mode ...".
>>
>> Even though asa matter of fact it looks like many users have issues that
>> get solved by disabling burst mode.
>>
>>> nor does it
>>> mention support for omitting horizontal front or back porch intervals. In
>>> particular, there is no indication that the device can operate with collapsed
>>> or suppressed horizontal blanking, as enabled by MIPI_DSI_MODE_VIDEO_BURST,
>>> MIPI_DSI_MODE_VIDEO_NO_HFP, or MIPI_DSI_MODE_VIDEO_NO_HBP.
>>
>> This is correct.
>>
>> We can still try to get TI feedback, but it that won't happen in, say, a
>> few weeks then I think we should apply this patch.
>>
>
> We have not received any further updates from TI regarding this issue, and
> at this point, we are not sure if we will get additional feedback from them.
> As you had mentioned earlier that the patch could be considered after
> waiting for some time, could you please let us know how we can proceed
> further from here?

I am getting some feedback from TI, but it is taking some time.

For the time being I think it is clear that HBP and HFP are required, and
so removing the MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP
in your patch seems to be fully correct, even though this had no effect on
the panel I tested.

I'm still trying to get some better info to ensure that switching from
burst mode to non-burst mode is not expected to have side effects.

For thi reason, I think it would be great if you could send a new version
with two separate patches: the first one enabling HFP and HBP and which can
be applied right away, the second to disable burst mode for which I'd wait
a bit longer for TI feedback. You can keep the Tested-by lines.

I understand this is painful and taking time, but it's important to ensure
as much as possible that the change won't introduce regressions on existing
hardware.

Luca

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