Re: [PATCH v6 09/14] drm/mediatek: Support "Pre-multiplied" alpha blending in Mixer

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

Hi, Shawn:

On Fri, 2024-03-22 at 13:28 +0800, Shawn Sung wrote:
> From: Hsiao Chien Sung <shawn.sung@mediatek.com>
> 
> Support "Pre-multiplied" blend mode on MediaTek's chips.
> Before this patch, only the "Coverage" mode is supported.
> 
> Please refer to the description of the commit
> "drm/mediatek: Support alpha blending in display driver"
> for more information.
> 
> Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_ethdr.c | 25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_ethdr.c
> b/drivers/gpu/drm/mediatek/mtk_ethdr.c
> index 6bf398850e85f..4b12ca285e84b 100644
> --- a/drivers/gpu/drm/mediatek/mtk_ethdr.c
> +++ b/drivers/gpu/drm/mediatek/mtk_ethdr.c
> @@ -5,6 +5,7 @@
>  
>  #include <drm/drm_fourcc.h>
>  #include <drm/drm_framebuffer.h>
> +#include <drm/drm_blend.h>
>  #include <linux/clk.h>
>  #include <linux/component.h>
>  #include <linux/of.h>
> @@ -35,6 +36,7 @@
>  #define MIX_SRC_L0_EN				BIT(0)
>  #define MIX_L_SRC_CON(n)		(0x28 + 0x18 * (n))
>  #define NON_PREMULTI_SOURCE			(2 << 12)
> +#define PREMULTI_SOURCE				(3 << 12)
>  #define MIX_L_SRC_SIZE(n)		(0x30 + 0x18 * (n))
>  #define MIX_L_SRC_OFFSET(n)		(0x34 + 0x18 * (n))
>  #define MIX_FUNC_DCM0			0x120
> @@ -153,7 +155,8 @@ void mtk_ethdr_layer_config(struct device *dev,
> unsigned int idx,
>  	struct mtk_plane_pending_state *pending = &state->pending;
>  	unsigned int offset = (pending->x & 1) << 31 | pending->y << 16
> | pending->x;
>  	unsigned int align_width = ALIGN_DOWN(pending->width, 2);
> -	unsigned int alpha_con = 0;
> +	unsigned int mix_con = NON_PREMULTI_SOURCE;

I think you should not assign here. You should choose one of
PREMULTI_SOURCE or NON_PREMULTI_SOURCE later.

> +	bool replace_src_a = false;
>  
>  	dev_dbg(dev, "%s+ idx:%d", __func__, idx);
>  
> @@ -170,19 +173,27 @@ void mtk_ethdr_layer_config(struct device *dev,
> unsigned int idx,
>  		return;
>  	}
>  
> -	if (state->base.fb && state->base.fb->format->has_alpha)
> -		alpha_con = MIXER_ALPHA_AEN | MIXER_ALPHA;
> +	mix_con |= MIXER_ALPHA_AEN | (state->base.alpha & MIXER_ALPHA);

Now support pixel alpha, and this seems to support plane alpha.
Separate this to another patch.

>  
> -	mtk_mmsys_mixer_in_config(priv->mmsys_dev, idx + 1, alpha_con ?
> false : true,
> -				  DEFAULT_9BIT_ALPHA,
> +	if (state->base.pixel_blend_mode != DRM_MODE_BLEND_COVERAGE)
> +		mix_con |= PREMULTI_SOURCE;
> +
> +	if (state->base.fb && !state->base.fb->format->has_alpha) {
> +		/*
> +		 * Mixer doesn't support CONST_BLD mode,
> +		 * use a trick to make the output equivalent
> +		 */
> +		replace_src_a = true;

Ditto.

Regards,
CK

> +	}
> +
> +	mtk_mmsys_mixer_in_config(priv->mmsys_dev, idx + 1,
> replace_src_a, MIXER_ALPHA,
>  				  pending->x & 1 ?
> MIXER_INX_MODE_EVEN_EXTEND :
>  				  MIXER_INX_MODE_BYPASS, align_width /
> 2 - 1, cmdq_pkt);
>  
>  	mtk_ddp_write(cmdq_pkt, pending->height << 16 | align_width,
> &mixer->cmdq_base,
>  		      mixer->regs, MIX_L_SRC_SIZE(idx));
>  	mtk_ddp_write(cmdq_pkt, offset, &mixer->cmdq_base, mixer->regs, 
> MIX_L_SRC_OFFSET(idx));
> -	mtk_ddp_write_mask(cmdq_pkt, alpha_con, &mixer->cmdq_base,
> mixer->regs, MIX_L_SRC_CON(idx),
> -			   0x1ff);
> +	mtk_ddp_write(cmdq_pkt, mix_con, &mixer->cmdq_base, mixer-
> >regs, MIX_L_SRC_CON(idx));
>  	mtk_ddp_write_mask(cmdq_pkt, BIT(idx), &mixer->cmdq_base,
> mixer->regs, MIX_SRC_CON,
>  			   BIT(idx));
>  }