Re: [PATCH v2 2/2] drm: lcdif: Wait for vblank before disabling DMA

Liu Ying
2026-04-07T06:33:13Z

Hi Paul,

On Thu, Apr 02, 2026 at 08:33:51PM +0200, Paul Kocialkowski wrote:
> It is necessary to wait for the full frame to finish streaming
> through the DMA engine before we can safely disable it by removing
> the DISP_PARA_DISP_ON bit. Disabling it in-flight can leave the
> hardware confused and unable to resume streaming for the next frame.
>
> This causes the FIFO underrun and empty status bits to be set and
> a single solid color to be shown on the display, coming from one of
> the pixels of the previous frame. The issue occurs sporadically when
> a new mode is set, which triggers the crtc disable and enable paths.
>
> Setting the shadow load bit and waiting for it to be cleared by the
> DMA engine allows waiting for completion.
>
> The NXP BSP driver addresses this issue with a hardcoded 25 ms sleep.
>
> Fixes: 9db35bb349a0 ("drm: lcdif: Add support for i.MX8MP LCDIF variant")
> Signed-off-by: Paul Kocialkowski <paulk@sys-base.io>
> Co-developed-by: Lucas Stach <l.stach@pengutronix.de>

There is a warning reported by checkpatch.pl:
WARNING: Co-developed-by: must be immediately followed by Signed-off-by:
#23:
Co-developed-by: Lucas Stach <l.stach@pengutronix.de>

With this fixed:
Acked-by: Liu Ying <victor.liu@nxp.com>
Thanks!

--
Regards,
Liu Ying