[PATCH v2] drm: rcar-du: Fix Alpha blending issue on Gen3

[Laurent Pinchart]

Hi Biju,

Thank you for the patch.

On Tue, Apr 26, 2022 at 09:41:57AM +0100, Biju Das wrote:
> From: LUU HOAI <hoai.luu.ub at renesas.com>
> 
> As per R-Car-Gen3_Common_OPC_Customer_Notifications_V30.1.pdf,
> unexpected image output(such as incorrect colors or planes being
> invisible) can happen on the below conditions, as PnALPHAR register
> is not initialized by reset.
> 
> When alpha blending (PpMRm.PpSPIM=0b101) is performed and:
> 	•two Planes are enabled on any DUn (n=0,1,2,3)
> 		oDSPRn= 0x0000 0031 or 0x0000 0013
> 	•or DU0 and DU1 is used for display at the same time
> 		oDSPR0= 0x0000 0001 and DSPR1= 0x0000 0003
> 		oDSPR0= 0x0000 0003 and DSPR1= 0x0000 0001
> 	•or DU2 and DU3(H3 Only) is used for display at the same time
> 		oDSPR2= 0x0000 0001 and DSPR3= 0x0000 0003
> 		oDSPR2= 0x0000 0003 and DSPR3= 0x0000 0001
> 
> This patch set PnALPHAR register to 0 to avoid this issue.
> 
> Signed-off-by: LUU HOAI <hoai.luu.ub at renesas.com>
> Signed-off-by: Biju Das <biju.das.jz at bp.renesas.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> ---
> v1->v2:
>  * Updated commit description
>  * Updated the code comments
> ---
>  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> index f214a8b6cfd3..aa80c44dd8d7 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> @@ -510,6 +510,18 @@ static void rcar_du_plane_setup_format_gen3(struct rcar_du_group *rgrp,
>  
>  	rcar_du_plane_write(rgrp, index, PnDDCR4,
>  			    state->format->edf | PnDDCR4_CODE);
> +
> +	/*
> +	 * On Gen3, some DU channels have two planes, each being wired to a
> +	 * separate VSPD instance. The DU can then blend two planes. While
> +	 * this feature isn't used by the driver, issues related to alpha
> +	 * blending (such as incorrect colors or planes being invisible) may
> +	 * still occur if the PnALPHAR register has a stale value. Set the
> +	 * register to 0 to avoid this.
> +	 */
> +
> +	/* TODO: Check if alpha-blending should be disabled in PnMR. */
> +	rcar_du_plane_write(rgrp, index, PnALPHAR, 0);
>  }
>  
>  static void rcar_du_plane_setup_format(struct rcar_du_group *rgrp,

-- 
Regards,

Laurent Pinchart