[PATCH 1/3] drm: lcdif: Set undocumented bit to clear FIFO at vsync

[Lucas Stach]

Am Dienstag, dem 31.03.2026 um 00:46 +0200 schrieb Paul Kocialkowski:
> There is an undocumented bit used in the NXP BSP to clear the FIFO
> systematically at vsync. In normal operation, the FIFO should already
> be empty but it doesn't hurt to add it as an extra safety measure.
> 
> Signed-off-by: Paul Kocialkowski <paulk at sys-base.io>

Reviewed-by: Lucas Stach <l.stach at pengutronix.de>

> ---
>  drivers/gpu/drm/mxsfb/lcdif_kms.c  | 3 ++-
>  drivers/gpu/drm/mxsfb/lcdif_regs.h | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> index ef3250a5c54f..a00c4f6d63f4 100644
> --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
> +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> @@ -338,7 +338,8 @@ static void lcdif_set_mode(struct lcdif_drm_private *lcdif, u32 bus_flags)
>  	 * Downstream set it to 256B burst size to improve the memory
>  	 * efficiency so set it here too.
>  	 */
> -	ctrl = CTRLDESCL0_3_P_SIZE(2) | CTRLDESCL0_3_T_SIZE(2) |
> +	ctrl = CTRLDESCL0_3_STATE_CLEAR_VSYNC |
> +	       CTRLDESCL0_3_P_SIZE(2) | CTRLDESCL0_3_T_SIZE(2) |
>  	       CTRLDESCL0_3_PITCH(lcdif->crtc.primary->state->fb->pitches[0]);
>  	writel(ctrl, lcdif->base + LCDC_V8_CTRLDESCL0_3);
>  }
> diff --git a/drivers/gpu/drm/mxsfb/lcdif_regs.h b/drivers/gpu/drm/mxsfb/lcdif_regs.h
> index c55dfb236c1d..17882c593d27 100644
> --- a/drivers/gpu/drm/mxsfb/lcdif_regs.h
> +++ b/drivers/gpu/drm/mxsfb/lcdif_regs.h
> @@ -190,6 +190,7 @@
>  #define CTRLDESCL0_1_WIDTH(n)		((n) & 0xffff)
>  #define CTRLDESCL0_1_WIDTH_MASK		GENMASK(15, 0)
>  
> +#define CTRLDESCL0_3_STATE_CLEAR_VSYNC	BIT(23)
>  #define CTRLDESCL0_3_P_SIZE(n)		(((n) << 20) & CTRLDESCL0_3_P_SIZE_MASK)
>  #define CTRLDESCL0_3_P_SIZE_MASK	GENMASK(22, 20)
>  #define CTRLDESCL0_3_T_SIZE(n)		(((n) << 16) & CTRLDESCL0_3_T_SIZE_MASK)