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

[Luca Ceresoli]

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

Luca

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