Am Montag, dem 21.06.2021 um 00:47 +0200 schrieb Marek Vasut:
> 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 <ma...@denx.de>
Reviewed-by: Lucas Stach <l.st...@pengutronix.de>
> Cc: Daniel Abrecht <pub...@danielabrecht.ch>
> Cc: Emil Velikov <emil.l.veli...@gmail.com>
> Cc: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
> Cc: Lucas Stach <l.st...@pengutronix.de>
> Cc: Stefan Agner <ste...@agner.ch>
> ---
> drivers/gpu/drm/mxsfb/mxsfb_kms.c | 29 +++++++++++++++++++++++++++++
> drivers/gpu/drm/mxsfb/mxsfb_regs.h | 1 +
> 2 files changed, 30 insertions(+)
>
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index 300e7bab0f43..01e0f525360f 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -115,6 +115,35 @@ static void mxsfb_enable_controller(struct
> mxsfb_drm_private *mxsfb)
> reg |= VDCTRL4_SYNC_SIGNALS_ON;
> writel(reg, mxsfb->base + LCDC_VDCTRL4);
>
> + /*
> + * Enable recovery on underflow.
> + *
> + * 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.
> + */
> + reg = readl(mxsfb->base + LCDC_CTRL1);
> + reg |= CTRL1_RECOVER_ON_UNDERFLOW;
> + writel(reg, mxsfb->base + LCDC_CTRL1);
> +
> writel(CTRL_RUN, mxsfb->base + LCDC_CTRL + REG_SET);
> }
>
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_regs.h
> b/drivers/gpu/drm/mxsfb/mxsfb_regs.h
> index 55d28a27f912..df90e960f495 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_regs.h
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_regs.h
> @@ -54,6 +54,7 @@
> #define CTRL_DF24 BIT(1)
> #define CTRL_RUN BIT(0)
>
> +#define CTRL1_RECOVER_ON_UNDERFLOW BIT(24)
> #define CTRL1_FIFO_CLEAR BIT(21)
> #define CTRL1_SET_BYTE_PACKAGING(x) (((x) & 0xf) << 16)
> #define CTRL1_GET_BYTE_PACKAGING(x) (((x) >> 16) & 0xf)
