Re: [PATCH v8 11/16] drm/mediatek: Support "Pre-multiplied" blending in OVL

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

Hi, Shawn:

On Thu, 2024-06-06 at 17:26 +0800, Shawn Sung wrote:
> From: Hsiao Chien Sung <shawn.sung@mediatek.com>
> 
> Support "Pre-multiplied" alpha blending mode on in OVL.
> Before this patch, only the "coverage" mode is supported.
> 
> Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_ovl.c | 40 +++++++++++++++++++++----
>  1 file changed, 34 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> index 54a6f11aa867..de1633988921 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> @@ -52,13 +52,16 @@
>  #define GMC_THRESHOLD_HIGH	((1 << GMC_THRESHOLD_BITS) / 4)
>  #define GMC_THRESHOLD_LOW	((1 << GMC_THRESHOLD_BITS) / 8)
>  
> +#define OVL_CON_CLRFMT_MAN	BIT(23)
>  #define OVL_CON_BYTE_SWAP	BIT(24)
> -#define OVL_CON_MTX_YUV_TO_RGB	(6 << 16)
> +#define OVL_CON_RGB_SWAP	BIT(25)
>  #define OVL_CON_CLRFMT_RGB	(1 << 12)
>  #define OVL_CON_CLRFMT_RGBA8888	(2 << 12)
>  #define OVL_CON_CLRFMT_ARGB8888	(3 << 12)
>  #define OVL_CON_CLRFMT_UYVY	(4 << 12)
>  #define OVL_CON_CLRFMT_YUYV	(5 << 12)
> +#define OVL_CON_MTX_YUV_TO_RGB	(6 << 16)
> +#define OVL_CON_CLRFMT_PARGB8888	(OVL_CON_CLRFMT_ARGB8888 | OVL_CON_CLRFMT_MAN)
>  #define OVL_CON_CLRFMT_RGB565(ovl)	((ovl)->data->fmt_rgb565_is_0 ? \
>  					0 : OVL_CON_CLRFMT_RGB)
>  #define OVL_CON_CLRFMT_RGB888(ovl)	((ovl)->data->fmt_rgb565_is_0 ? \
> @@ -72,6 +75,8 @@
>  #define	OVL_CON_VIRT_FLIP	BIT(9)
>  #define	OVL_CON_HORZ_FLIP	BIT(10)
>  
> +#define OVL_COLOR_ALPHA		GENMASK(31, 24)
> +
>  static inline bool is_10bit_rgb(u32 fmt)
>  {
>  	switch (fmt) {
> @@ -296,7 +301,13 @@ void mtk_ovl_config(struct device *dev, unsigned int w,
>  	if (w != 0 && h != 0)
>  		mtk_ddp_write_relaxed(cmdq_pkt, h << 16 | w, &ovl->cmdq_reg, ovl->regs,
>  				      DISP_REG_OVL_ROI_SIZE);
> -	mtk_ddp_write_relaxed(cmdq_pkt, 0x0, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_ROI_BGCLR);
> +
> +	/*
> +	 * The background color must be opaque black (ARGB),
> +	 * otherwise the alpha blending will have no effect
> +	 */
> +	mtk_ddp_write_relaxed(cmdq_pkt, OVL_COLOR_ALPHA, &ovl->cmdq_reg,
> +			      ovl->regs, DISP_REG_OVL_ROI_BGCLR);

The coverage mode formula is:
dst.RGB = src.RGB * src.A + dst.RGB * (1 - src.A)

The pre-multiplied mode formula is:
dst.RGB = src.RGB + dst.RGB * (1 - src.A)

Both formula has no destination alpha (I think background color is last destination),
why coverage mode work fine but pre-multiplied mode has something wrong?

>  
>  	mtk_ddp_write(cmdq_pkt, 0x1, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_RST);
>  	mtk_ddp_write(cmdq_pkt, 0x0, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_RST);
> @@ -372,7 +383,8 @@ void mtk_ovl_layer_off(struct device *dev, unsigned int idx,
>  		      DISP_REG_OVL_RDMA_CTRL(idx));
>  }
>  
> -static unsigned int ovl_fmt_convert(struct mtk_disp_ovl *ovl, unsigned int fmt)
> +static unsigned int ovl_fmt_convert(struct mtk_disp_ovl *ovl, unsigned int fmt,
> +				    unsigned int blend_mode)
>  {
>  	/* The return value in switch "MEM_MODE_INPUT_FORMAT_XXX"
>  	 * is defined in mediatek HW data sheet.
> @@ -391,21 +403,35 @@ static unsigned int ovl_fmt_convert(struct mtk_disp_ovl *ovl, unsigned int fmt)
>  		return OVL_CON_CLRFMT_RGB888(ovl) | OVL_CON_BYTE_SWAP;
>  	case DRM_FORMAT_RGBX8888:
>  	case DRM_FORMAT_RGBA8888:
> +		return blend_mode == DRM_MODE_BLEND_COVERAGE ?
> +		       OVL_CON_CLRFMT_ARGB8888 :
> +		       OVL_CON_CLRFMT_PARGB8888;
>  	case DRM_FORMAT_RGBX1010102:
>  	case DRM_FORMAT_RGBA1010102:
>  		return OVL_CON_CLRFMT_ARGB8888;
>  	case DRM_FORMAT_BGRX8888:
>  	case DRM_FORMAT_BGRA8888:
> +		return OVL_CON_BYTE_SWAP |
> +		       (blend_mode == DRM_MODE_BLEND_COVERAGE ?
> +		       OVL_CON_CLRFMT_ARGB8888 :
> +		       OVL_CON_CLRFMT_PARGB8888);
>  	case DRM_FORMAT_BGRX1010102:
>  	case DRM_FORMAT_BGRA1010102:
>  		return OVL_CON_CLRFMT_ARGB8888 | OVL_CON_BYTE_SWAP;
>  	case DRM_FORMAT_XRGB8888:
>  	case DRM_FORMAT_ARGB8888:
> +		return blend_mode == DRM_MODE_BLEND_COVERAGE ?
> +		       OVL_CON_CLRFMT_RGBA8888 :
> +		       OVL_CON_CLRFMT_PARGB8888;

In pre-multiplied mode, DRM_FORMAT_RGBA8888 and DRM_FORMAT_ARGB8888 would return the same value OVL_CON_CLRFMT_PARGB8888,
so how does hardware distinguish these two format?

>  	case DRM_FORMAT_XRGB2101010:
>  	case DRM_FORMAT_ARGB2101010:
>  		return OVL_CON_CLRFMT_RGBA8888;
>  	case DRM_FORMAT_XBGR8888:
>  	case DRM_FORMAT_ABGR8888:
> +		return OVL_CON_RGB_SWAP |
> +		       (blend_mode == DRM_MODE_BLEND_COVERAGE ?
> +		       OVL_CON_CLRFMT_RGBA8888 :
> +		       OVL_CON_CLRFMT_PARGB8888);

Originally, DRM_MODE_BLEND_COVERAGE and DRM_FORMAT_ABGR8888 would return

OVL_CON_CLRFMT_RGBA8888 | OVL_CON_BYTE_SWAP

but this patch return

OVL_CON_CLRFMT_RGBA8888 | OVL_CON_RGB_SWAP

This is not related to pre-multiplied, so separate this to another patch.


>  	case DRM_FORMAT_XBGR2101010:
>  	case DRM_FORMAT_ABGR2101010:
>  		return OVL_CON_CLRFMT_RGBA8888 | OVL_CON_BYTE_SWAP;
> @@ -448,9 +474,11 @@ void mtk_ovl_layer_config(struct device *dev, unsigned int idx,
>  		return;
>  	}
>  
> -	con = ovl_fmt_convert(ovl, fmt);
> -	if (state->base.fb && state->base.fb->format->has_alpha)
> -		con |= OVL_CON_AEN | OVL_CON_ALPHA;
> +	con = ovl_fmt_convert(ovl, fmt, blend_mode);
> +	if (state->base.fb) {
> +		con |= OVL_CON_AEN;
> +		con |= state->base.alpha & OVL_CON_ALPHA;

This modification is to support constant alpha, not related to pre-multiplied alpha. So separate this to another patch.

Regards,
CK

> +	}
>  
>  	/* CONST_BLD must be enabled for XRGB formats although the alpha channel
>  	 * can be ignored, or OVL will still read the value from memory.
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