[PATCH] drm: mxsfb: Enable recovery on underflow

[Jagan Teki]

On Mon, Jun 21, 2021 at 4:17 AM Marek Vasut <marex at denx.de> wrote:
>
> There is some sort of corner case behavior of the controller,
> which could rarely be triggered at least on i.MX6SX connected
> to 800x480 DPI panel and i.MX8MM connected to DPI->DSI->LVDS
> bridged 1920x1080 panel (and likely on other setups too), where
> the image on the panel shifts to the right and wraps around.
> This happens either when the controller is enabled on boot or
> even later during run time. The condition does not correct
> itself automatically, i.e. the display image remains shifted.
>
> It seems this problem is known and is due to sporadic underflows
> of the LCDIF FIFO. While the LCDIF IP does have underflow/overflow
> IRQs, neither of the IRQs trigger and neither IRQ status bit is
> asserted when this condition occurs.
>
> All known revisions of the LCDIF IP have CTRL1 RECOVER_ON_UNDERFLOW
> bit, which is described in the reference manual since i.MX23 as
> "
>   Set this bit to enable the LCDIF block to recover in the next
>   field/frame if there was an underflow in the current field/frame.
> "
> Enable this bit to mitigate the sporadic underflows.
>
> Fixes: 45d59d704080 ("drm: Add new driver for MXSFB controller")
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Daniel Abrecht <public at danielabrecht.ch>
> Cc: Emil Velikov <emil.l.velikov at gmail.com>
> Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Cc: Lucas Stach <l.stach at pengutronix.de>
> Cc: Stefan Agner <stefan at agner.ch>
> ---

Reviewed-by: Jagan Teki <jagan at amarulasolutions.com>