[PATCH v3 3/8] drm: lcdif: enable DMA before display

[Ying Liu]

On Thursday, September 28, 2023 7:36 PM, Lucas Stach <l.stach at pengutronix.de> wrote:
> Otherwise the DMA enable races with the fetch start, which causes
> wrong or no data to be scanned out on the first frame. Also there
> is no point in waiting for the DMA disable when the controller is
> going to shut down. Simply disable the display first so no further
> fetches are triggered and then shut down DMA.
> 
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
> ---
> v3: new patch
> ---
>  drivers/gpu/drm/mxsfb/lcdif_kms.c | 23 ++++++++---------------
>  1 file changed, 8 insertions(+), 15 deletions(-)

It seems that this one is the key to make fb pixel format change
work ok for i.MX8mp LCDIF with modetest.  However, there is about
20% probability to show constant color with the same test running
on i.MX93 LCDIF.  On top of this patch series, duplicating plane update
in crtc atomic_enable like downstream driver does seems avoid the
issue for i.MX93.

Regards,
Liu Ying