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

[Luca Ceresoli]

On Wed Apr 15, 2026 at 9:13 AM CEST, Luca Ceresoli wrote:
> Hello Sudarshan,
>
> On Sun Apr 12, 2026 at 7:38 AM CEST, Sudarshan Shetty wrote:
>> The current DSI mode configuration enables VIDEO_BURST and disables
>> horizontal front porch (HFP) and back porch (HBP) transmission using
>> MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP.
>>
>> However, the SN65DSI83/84 bridge relies on receiving full horizontal
>> timing information over DSI in order to correctly reconstruct the LVDS
>> output timings. When HFP and HBP are not transmitted, the bridge cannot
>> recreate the required timing parameters, resulting in unstable or
>> missing display output on some panels.
>>
>> Additionally, while burst mode is supported by the hardware, its use
>> depends on continuous clock behavior from the DSI host. In practice,
>> burst mode may introduce instability depending on the host controller
>> implementation, as the DSI link may transition to low-power state
>> between bursts.
>>
>> In testing, removing burst mode and ensuring full horizontal timing
>> transmission results in stable LVDS output across affected panels.
>>
>> Update the DSI mode flags to:
>>   - Drop MIPI_DSI_MODE_VIDEO_BURST
>>   - Drop MIPI_DSI_MODE_VIDEO_NO_HFP
>>   - Drop MIPI_DSI_MODE_VIDEO_NO_HBP
>>
>> This aligns with common system configurations where non-burst mode is
>> preferred and full timing information is transmitted over DSI.
>>
>> Signed-off-by: Sudarshan Shetty <tessolveupstream@xxxxxxxxx>
>
> Thanks for having gone into the details and provide a good explanation for
> the removal of these three flags.
>
> It would be still great to have authoritative info from TI, possibly as an
> update to the documentation.
>
> I managed to test on a board with i.MX93, a TI SN65DSI84 and a 1920x1080p60
> panel, and:
>
>  - no image shown with the current mainline driver
>  - it works by removing only MIPI_DSI_MODE_VIDEO_BURST (my current setup)
>  - it works with this patch applied
>
> Tested-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx> # imx93 1920x1080p60

And tested on a i.MX8MP board too, with a different 1920x1080p60
panel. This one was working without the patch and is equally working with
the patch applied.

Tested-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx> # imx8mp 1920x1080p60

Luca

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