Re: [PATCH v4 13/19] drm/mediatek: Export OVL Blend function

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

On Thu, 2025-08-28 at 16:07 +0800, Paul Chen wrote:
> From: Paul-pl Chen <paul-pl.chen@mediatek.com>
> 
> For the new BLENDER component, the OVL ignore pixel alpha logic
> should be exported as a function and reused it.
> 
> Signed-off-by: Nancy Lin <nancy.lin@mediatek.com>
> Signed-off-by: Paul-pl Chen <paul-pl.chen@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_ovl.c | 68 +++++++++++++++++--------
>  drivers/gpu/drm/mediatek/mtk_disp_ovl.h |  8 +++
>  2 files changed, 56 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> index e3ee3f60f4ba..7cd3978beb98 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> @@ -228,6 +228,23 @@ void mtk_ovl_disable_vblank(struct device *dev)
>  	writel_relaxed(0x0, ovl->regs + DISP_REG_OVL_INTEN);
>  }
>  
> +bool mtk_ovl_is_ignore_pixel_alpha(struct mtk_plane_state *state, unsigned int blend_mode)
> +{
> +	if (!state->base.fb)
> +		return false;
> +
> +	/*
> +	 * Although the alpha channel can be ignored, CONST_BLD must be enabled
> +	 * for XRGB format, otherwise OVL will still read the value from memory.
> +	 * For RGB888 related formats, whether CONST_BLD is enabled or not won't
> +	 * affect the result. Therefore we use !has_alpha as the condition.
> +	 */
> +	if (blend_mode == DRM_MODE_BLEND_PIXEL_NONE || !state->base.fb->format->has_alpha)
> +		return true;
> +
> +	return false;
> +}
> +
>  u32 mtk_ovl_get_blend_modes(struct device *dev)
>  {
>  	struct mtk_disp_ovl *ovl = dev_get_drvdata(dev);
> @@ -414,6 +431,29 @@ void mtk_ovl_layer_off(struct device *dev, unsigned int idx,
>  		      DISP_REG_OVL_RDMA_CTRL(idx));
>  }
>  
> +unsigned int mtk_ovl_get_blend_mode(struct mtk_plane_state *state, unsigned int blend_modes)
> +{
> +	unsigned int blend_mode = DRM_MODE_BLEND_COVERAGE;
> +
> +	/*
> +	 * For the platforms where OVL_CON_CLRFMT_MAN is defined in the hardware data sheet
> +	 * and supports premultiplied color formats, such as OVL_CON_CLRFMT_PARGB888
> +	 * and supports premultiplied color formats, such as OVL_CON_CLRFMT_PARGB8888.
> +	 *
> +	 * Check blend_modes in the driver data to see if premultiplied mode is supported.
> +	 * If not, use coverage mode instead to set it to the supported color formats.
> +	 *
> +	 * Current DRM assumption is that alpha is default premultiplied, so the bitmask of
> +	 * blend_modes must include BIT(DRM_MODE_BLEND_PREMULTI). Otherwise, mtk_plane_init()
> +	 * will get an error return from drm_plane_create_blend_mode_property() and
> +	 * state->base.pixel_blend_mode should not be used.
> +	 */
> +	if (blend_modes & BIT(DRM_MODE_BLEND_PREMULTI))
> +		blend_mode = state->base.pixel_blend_mode;
> +
> +	return blend_mode;
> +}
> +
>  unsigned int mtk_ovl_fmt_convert(unsigned int fmt, unsigned int blend_mode,
>  				 bool fmt_rgb565_is_0, bool color_convert,
>  				 u8 clrfmt_shift, u32 clrfmt_man, u32 byte_swap, u32 rgb_swap)
> @@ -541,7 +581,7 @@ void mtk_ovl_layer_config(struct device *dev, unsigned int idx,
>  	unsigned int rotation = pending->rotation;
>  	unsigned int offset = (pending->y << 16) | pending->x;
>  	unsigned int src_size = (pending->height << 16) | pending->width;
> -	unsigned int blend_mode = state->base.pixel_blend_mode;
> +	unsigned int blend_mode = mtk_ovl_get_blend_mode(state, ovl->data->blend_modes);

Why you change behavior here?
Originally, 'blend_mode = state->base.pixel_blend_mode' directly.
But this patch add a check and blend_mode may be DRM_MODE_BLEND_COVERAGE.
The behavior changes. Why change this behavior?

>  	unsigned int ignore_pixel_alpha = 0;
>  	unsigned int con;
>  
> @@ -566,17 +606,8 @@ void mtk_ovl_layer_config(struct device *dev, unsigned int idx,
>  		 * For blend_modes supported SoCs, always enable alpha blending.
>  		 * For blend_modes unsupported SoCs, enable alpha blending when has_alpha is set.
>  		 */
> -		if (blend_mode || state->base.fb->format->has_alpha)
> +		if (state->base.pixel_blend_mode || state->base.fb->format->has_alpha)
>  			con |= OVL_CON_AEN;
> -
> -		/*
> -		 * Although the alpha channel can be ignored, CONST_BLD must be enabled
> -		 * for XRGB format, otherwise OVL will still read the value from memory.
> -		 * For RGB888 related formats, whether CONST_BLD is enabled or not won't
> -		 * affect the result. Therefore we use !has_alpha as the condition.
> -		 */
> -		if (blend_mode == DRM_MODE_BLEND_PIXEL_NONE || !state->base.fb->format->has_alpha)
> -			ignore_pixel_alpha = OVL_CONST_BLEND;
>  	}
>  
>  	/*
> @@ -602,6 +633,9 @@ void mtk_ovl_layer_config(struct device *dev, unsigned int idx,
>  
>  	mtk_ddp_write_relaxed(cmdq_pkt, con, &ovl->cmdq_reg, ovl->regs,
>  			      DISP_REG_OVL_CON(idx));
> +
> +	if (mtk_ovl_is_ignore_pixel_alpha(state, blend_mode))
> +		ignore_pixel_alpha = OVL_CONST_BLEND;
>  	mtk_ddp_write_relaxed(cmdq_pkt, pitch_lsb | ignore_pixel_alpha,
>  			      &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_PITCH(idx));
>  	mtk_ddp_write_relaxed(cmdq_pkt, src_size, &ovl->cmdq_reg, ovl->regs,