On 19-05-2026 17:13, Luca Ceresoli wrote:
> 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.
>
Thanks for the clarification. I just wanted to confirm my understanding
regarding the patch split you suggested.
>From your comments, my understanding is that the first patch would only
enable HFP and HBP by removing MIPI_DSI_MODE_VIDEO_NO_HFP and
MIPI_DSI_MODE_VIDEO_NO_HBP, while keeping burst mode enabled, so the mode
flags would become:
dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST |
MIPI_DSI_MODE_VIDEO_NO_HSA | MIPI_DSI_MODE_NO_EOT_PACKET;
Then, the second patch would only disable burst mode, resulting in:
dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_NO_HSA |
MIPI_DSI_MODE_NO_EOT_PACKET;
Could you please confirm whether my understanding is correct?
Also, from our testing, when using:
dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST |
MIPI_DSI_MODE_VIDEO_NO_HSA | MIPI_DSI_MODE_NO_EOT_PACKET;
we are not able to get display output. I just wanted to mention this
observation in case it is relevant to the patch split discussion.
Additionally, regarding the Tested-by tags you mentioned earlier,
should I carry them forward to both patches, or would you prefer them
only on the applicable patch?
> 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
