[PATCH RESEND 0/2] drm/msm/dpu: use full scale alpha in generic code

[PATCH RESEND 0/2] drm/msm/dpu: use full scale alpha in generic code

[Dmitry Baryshkov]

Both _dpu_crtc_setup_blend_cfg() and setup_blend_config_alpha()
callbacks embed knowledge about platform's alpha range (8-bit or
10-bit). Make _dpu_crtc_setup_blend_cfg() use full 16-bit values for
alpha and reduce alpha only in DPU-specific callbacks.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
Dmitry Baryshkov (2):
      drm/msm/dpu: simplify bg_alpha selection
      drm/msm/dpu: use full scale alpha in _dpu_crtc_setup_blend_cfg()

 drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c  | 18 +++++++-----------
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_lm.c | 10 ++++++----
 2 files changed, 13 insertions(+), 15 deletions(-)
---
base-commit: a933d3dc1968fcfb0ab72879ec304b1971ed1b9a
change-id: 20250814-dpu-rework-alpha-060ff6bf5185

Best regards,
-- 
With best wishes
Dmitry

[PATCH RESEND 1/2] drm/msm/dpu: simplify bg_alpha selection

[Dmitry Baryshkov]

In order to be more obvious in fg_alpha / bg_alpha handling during the
blending programming drop the default setting for background alpha value
and set it explicitly in all cases.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index d4b545448d74657aafc96e9042c7756654b4f0e7..651159e8731194d75b52c05158bfd1c9bad8b10c 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -335,13 +335,13 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 		max_alpha = 0x3ff;
 		fg_alpha = pstate->base.alpha >> 6;
 	}
-	bg_alpha = max_alpha - fg_alpha;
 
 	/* default to opaque blending */
 	if (pstate->base.pixel_blend_mode == DRM_MODE_BLEND_PIXEL_NONE ||
 	    !format->alpha_enable) {
 		blend_op = DPU_BLEND_FG_ALPHA_FG_CONST |
 			DPU_BLEND_BG_ALPHA_BG_CONST;
+		bg_alpha = max_alpha - fg_alpha;
 	} else if (pstate->base.pixel_blend_mode == DRM_MODE_BLEND_PREMULTI) {
 		blend_op = DPU_BLEND_FG_ALPHA_FG_CONST |
 			DPU_BLEND_BG_ALPHA_FG_PIXEL;
@@ -350,6 +350,7 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 			blend_op |= DPU_BLEND_BG_MOD_ALPHA |
 				    DPU_BLEND_BG_INV_MOD_ALPHA;
 		} else {
+			bg_alpha = 0;
 			blend_op |= DPU_BLEND_BG_INV_ALPHA;
 		}
 	} else {
@@ -363,6 +364,7 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 				    DPU_BLEND_BG_MOD_ALPHA |
 				    DPU_BLEND_BG_INV_MOD_ALPHA;
 		} else {
+			bg_alpha = 0;
 			blend_op |= DPU_BLEND_BG_INV_ALPHA;
 		}
 	}

-- 
2.47.3

Re: [PATCH RESEND 1/2] drm/msm/dpu: simplify bg_alpha selection

[Konrad Dybcio]

On 11/18/25 3:51 PM, Dmitry Baryshkov wrote:
> In order to be more obvious in fg_alpha / bg_alpha handling during the
> blending programming drop the default setting for background alpha value
> and set it explicitly in all cases.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---

Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>

Konrad

[PATCH RESEND 2/2] drm/msm/dpu: use full scale alpha in _dpu_crtc_setup_blend_cfg()

[Dmitry Baryshkov]

Both _dpu_crtc_setup_blend_cfg() and setup_blend_config_alpha()
callbacks embed knowledge about platform's alpha range (8-bit or
10-bit). Make _dpu_crtc_setup_blend_cfg() use full 16-bit values for
alpha and reduce alpha only in DPU-specific callbacks.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c  | 16 +++++-----------
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_lm.c | 10 ++++++----
 2 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index 651159e8731194d75b52c05158bfd1c9bad8b10c..a280c136104added1dbb2b432f15680bc1d5bd36 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -326,26 +326,20 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 {
 	struct dpu_hw_mixer *lm = mixer->hw_lm;
 	u32 blend_op;
-	u32 fg_alpha, bg_alpha, max_alpha;
+	u32 fg_alpha, bg_alpha;
 
-	if (mdss_ver->core_major_ver < 12) {
-		max_alpha = 0xff;
-		fg_alpha = pstate->base.alpha >> 8;
-	} else {
-		max_alpha = 0x3ff;
-		fg_alpha = pstate->base.alpha >> 6;
-	}
+	fg_alpha = pstate->base.alpha;
 
 	/* default to opaque blending */
 	if (pstate->base.pixel_blend_mode == DRM_MODE_BLEND_PIXEL_NONE ||
 	    !format->alpha_enable) {
 		blend_op = DPU_BLEND_FG_ALPHA_FG_CONST |
 			DPU_BLEND_BG_ALPHA_BG_CONST;
-		bg_alpha = max_alpha - fg_alpha;
+		bg_alpha = DRM_BLEND_ALPHA_OPAQUE - fg_alpha;
 	} else if (pstate->base.pixel_blend_mode == DRM_MODE_BLEND_PREMULTI) {
 		blend_op = DPU_BLEND_FG_ALPHA_FG_CONST |
 			DPU_BLEND_BG_ALPHA_FG_PIXEL;
-		if (fg_alpha != max_alpha) {
+		if (fg_alpha != DRM_BLEND_ALPHA_OPAQUE) {
 			bg_alpha = fg_alpha;
 			blend_op |= DPU_BLEND_BG_MOD_ALPHA |
 				    DPU_BLEND_BG_INV_MOD_ALPHA;
@@ -357,7 +351,7 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 		/* coverage blending */
 		blend_op = DPU_BLEND_FG_ALPHA_FG_PIXEL |
 			DPU_BLEND_BG_ALPHA_FG_PIXEL;
-		if (fg_alpha != max_alpha) {
+		if (fg_alpha != DRM_BLEND_ALPHA_OPAQUE) {
 			bg_alpha = fg_alpha;
 			blend_op |= DPU_BLEND_FG_MOD_ALPHA |
 				    DPU_BLEND_FG_INV_MOD_ALPHA |
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_lm.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_lm.c
index e8a76d5192c230fd64d748634ca8574a59aac02c..fb8c94fdb829be6f89bfcc6c5a83fdbd27778bf2 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_lm.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_lm.c
@@ -139,7 +139,8 @@ static void dpu_hw_lm_setup_blend_config_combined_alpha(struct dpu_hw_mixer *ctx
 	if (WARN_ON(stage_off < 0))
 		return;
 
-	const_alpha = (bg_alpha & 0xFF) | ((fg_alpha & 0xFF) << 16);
+	const_alpha = ((bg_alpha >> 8) & 0xff) |
+		(((fg_alpha >> 8) & 0xff) << 16);
 	DPU_REG_WRITE(c, LM_BLEND0_CONST_ALPHA + stage_off, const_alpha);
 	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
 }
@@ -160,7 +161,8 @@ dpu_hw_lm_setup_blend_config_combined_alpha_v12(struct dpu_hw_mixer *ctx,
 	if (WARN_ON(stage_off < 0))
 		return;
 
-	const_alpha = (bg_alpha & 0x3ff) | ((fg_alpha & 0x3ff) << 16);
+	const_alpha = ((bg_alpha >> 6) & 0x3ff) |
+		(((fg_alpha >> 6) & 0x3ff) << 16);
 	DPU_REG_WRITE(c, LM_BLEND0_CONST_ALPHA_V12 + stage_off, const_alpha);
 	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
 }
@@ -178,8 +180,8 @@ static void dpu_hw_lm_setup_blend_config(struct dpu_hw_mixer *ctx,
 	if (WARN_ON(stage_off < 0))
 		return;
 
-	DPU_REG_WRITE(c, LM_BLEND0_FG_ALPHA + stage_off, fg_alpha);
-	DPU_REG_WRITE(c, LM_BLEND0_BG_ALPHA + stage_off, bg_alpha);
+	DPU_REG_WRITE(c, LM_BLEND0_FG_ALPHA + stage_off, fg_alpha >> 8);
+	DPU_REG_WRITE(c, LM_BLEND0_BG_ALPHA + stage_off, bg_alpha >> 8);
 	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
 }
 

-- 
2.47.3

Re: [PATCH RESEND 2/2] drm/msm/dpu: use full scale alpha in _dpu_crtc_setup_blend_cfg()

[Konrad Dybcio]

On 11/18/25 3:51 PM, Dmitry Baryshkov wrote:
> Both _dpu_crtc_setup_blend_cfg() and setup_blend_config_alpha()
> callbacks embed knowledge about platform's alpha range (8-bit or
> 10-bit). Make _dpu_crtc_setup_blend_cfg() use full 16-bit values for
> alpha and reduce alpha only in DPU-specific callbacks.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---

[...]

> -	const_alpha = (bg_alpha & 0xFF) | ((fg_alpha & 0xFF) << 16);
> +	const_alpha = ((bg_alpha >> 8) & 0xff) |
> +		(((fg_alpha >> 8) & 0xff) << 16);

This begs for some bitfield.h

Konrad

>  	DPU_REG_WRITE(c, LM_BLEND0_CONST_ALPHA + stage_off, const_alpha);
>  	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
>  }
> @@ -160,7 +161,8 @@ dpu_hw_lm_setup_blend_config_combined_alpha_v12(struct dpu_hw_mixer *ctx,
>  	if (WARN_ON(stage_off < 0))
>  		return;
>  
> -	const_alpha = (bg_alpha & 0x3ff) | ((fg_alpha & 0x3ff) << 16);
> +	const_alpha = ((bg_alpha >> 6) & 0x3ff) |
> +		(((fg_alpha >> 6) & 0x3ff) << 16);
>  	DPU_REG_WRITE(c, LM_BLEND0_CONST_ALPHA_V12 + stage_off, const_alpha);
>  	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
>  }
> @@ -178,8 +180,8 @@ static void dpu_hw_lm_setup_blend_config(struct dpu_hw_mixer *ctx,
>  	if (WARN_ON(stage_off < 0))
>  		return;
>  
> -	DPU_REG_WRITE(c, LM_BLEND0_FG_ALPHA + stage_off, fg_alpha);
> -	DPU_REG_WRITE(c, LM_BLEND0_BG_ALPHA + stage_off, bg_alpha);
> +	DPU_REG_WRITE(c, LM_BLEND0_FG_ALPHA + stage_off, fg_alpha >> 8);
> +	DPU_REG_WRITE(c, LM_BLEND0_BG_ALPHA + stage_off, bg_alpha >> 8);
>  	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
>  }
>  
> 

Re: [PATCH RESEND 2/2] drm/msm/dpu: use full scale alpha in _dpu_crtc_setup_blend_cfg()

[Dmitry Baryshkov]

On Tue, Nov 18, 2025 at 04:02:03PM +0100, Konrad Dybcio wrote:
> On 11/18/25 3:51 PM, Dmitry Baryshkov wrote:
> > Both _dpu_crtc_setup_blend_cfg() and setup_blend_config_alpha()
> > callbacks embed knowledge about platform's alpha range (8-bit or
> > 10-bit). Make _dpu_crtc_setup_blend_cfg() use full 16-bit values for
> > alpha and reduce alpha only in DPU-specific callbacks.
> > 
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> > ---
> 
> [...]
> 
> > -	const_alpha = (bg_alpha & 0xFF) | ((fg_alpha & 0xFF) << 16);
> > +	const_alpha = ((bg_alpha >> 8) & 0xff) |
> > +		(((fg_alpha >> 8) & 0xff) << 16);
> 
> This begs for some bitfield.h

Which one(s) would you recommend? Ideally it should be something like
'get N top bits', but I don't see one.

> Konrad
> 
> >  	DPU_REG_WRITE(c, LM_BLEND0_CONST_ALPHA + stage_off, const_alpha);
> >  	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
> >  }
> > @@ -160,7 +161,8 @@ dpu_hw_lm_setup_blend_config_combined_alpha_v12(struct dpu_hw_mixer *ctx,
> >  	if (WARN_ON(stage_off < 0))
> >  		return;
> >  
> > -	const_alpha = (bg_alpha & 0x3ff) | ((fg_alpha & 0x3ff) << 16);
> > +	const_alpha = ((bg_alpha >> 6) & 0x3ff) |
> > +		(((fg_alpha >> 6) & 0x3ff) << 16);
> >  	DPU_REG_WRITE(c, LM_BLEND0_CONST_ALPHA_V12 + stage_off, const_alpha);
> >  	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
> >  }
> > @@ -178,8 +180,8 @@ static void dpu_hw_lm_setup_blend_config(struct dpu_hw_mixer *ctx,
> >  	if (WARN_ON(stage_off < 0))
> >  		return;
> >  
> > -	DPU_REG_WRITE(c, LM_BLEND0_FG_ALPHA + stage_off, fg_alpha);
> > -	DPU_REG_WRITE(c, LM_BLEND0_BG_ALPHA + stage_off, bg_alpha);
> > +	DPU_REG_WRITE(c, LM_BLEND0_FG_ALPHA + stage_off, fg_alpha >> 8);
> > +	DPU_REG_WRITE(c, LM_BLEND0_BG_ALPHA + stage_off, bg_alpha >> 8);
> >  	DPU_REG_WRITE(c, LM_BLEND0_OP + stage_off, blend_op);
> >  }
> >  
> > 

-- 
With best wishes
Dmitry

Re: [PATCH RESEND 2/2] drm/msm/dpu: use full scale alpha in _dpu_crtc_setup_blend_cfg()

[Konrad Dybcio]

On 11/19/25 8:50 AM, Dmitry Baryshkov wrote:
> On Tue, Nov 18, 2025 at 04:02:03PM +0100, Konrad Dybcio wrote:
>> On 11/18/25 3:51 PM, Dmitry Baryshkov wrote:
>>> Both _dpu_crtc_setup_blend_cfg() and setup_blend_config_alpha()
>>> callbacks embed knowledge about platform's alpha range (8-bit or
>>> 10-bit). Make _dpu_crtc_setup_blend_cfg() use full 16-bit values for
>>> alpha and reduce alpha only in DPU-specific callbacks.
>>>
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
>>> ---
>>
>> [...]
>>
>>> -	const_alpha = (bg_alpha & 0xFF) | ((fg_alpha & 0xFF) << 16);
>>> +	const_alpha = ((bg_alpha >> 8) & 0xff) |
>>> +		(((fg_alpha >> 8) & 0xff) << 16);
>>
>> This begs for some bitfield.h
> 
> Which one(s) would you recommend? Ideally it should be something like
> 'get N top bits', but I don't see one.

Perhaps we can create one.. there's include/linux/wordpart.h
with upper/lower_16/32_bits().. Maybe we could add

#define lower_n_bits(x, n) (FIELD_GET(GENMASK((n - 1), 0), x)

// register def
#define CONST_ALPHA_BG	GENMASK(,)
#define CONST_ALPHA_FG	GENMASK(,)

const_alpha = FIELD_GET(CONST_ALPHA_BG, lower_n_bits(bg_alpha, 8)) |
	      FIELD_GET(CONST_ALPHA_FG, lower_n_bits(fg_alpha, 8));

At which point it arguably becomes equally difficult to read.. but I
think the rule of thumb is that syntax sugar is better than raw bitops ;)

Konrad