drm_fb_xrgb8888_to_gray2() works like and share much code with
drm_fb_xrgb8888_to_mono(), but converts XRGB8888 to
2bit grayscale instead.

It uses drm_fb_xrgb8888_to_gray8() to convert the pixels to gray8 as an
intermediate step before converting to gray2.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---
 drivers/gpu/drm/drm_format_helper.c | 148 ++++++++++++++++++++++++++----------
 include/drm/drm_format_helper.h     |   4 +
 2 files changed, 110 insertions(+), 42 deletions(-)

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 8f3daf38ca639d3d39742c2c9fa0c54a3a9297a5..2f2171b3df609263cc9ce6809bf6144028c25380 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -1253,6 +1253,25 @@ int drm_fb_blit(struct iosys_map *dst, const unsigned int *dst_pitch, uint32_t d
 }
 EXPORT_SYMBOL(drm_fb_blit);
 
+static void drm_fb_gray8_to_gray2_line(void *dbuf, const void *sbuf, unsigned int pixels)
+{
+	u8 *dbuf8 = dbuf;
+	const u8 *sbuf8 = sbuf;
+	u8 px;
+
+	while (pixels) {
+		unsigned int i, bits = min(pixels, 4U);
+		u8 byte = 0;
+
+		for (i = 0; i < bits; i++, pixels--) {
+			byte >>= 2;
+			px = (*sbuf8++ * 3 + 127) / 255;
+			byte |= (px &= 0x03) << 6;
+		}
+		*dbuf8++ = byte;
+	}
+}
+
 static void drm_fb_gray8_to_mono_line(void *dbuf, const void *sbuf, unsigned int pixels)
 {
 	u8 *dbuf8 = dbuf;
@@ -1270,40 +1289,11 @@ static void drm_fb_gray8_to_mono_line(void *dbuf, const void *sbuf, unsigned int
 	}
 }
 
-/**
- * drm_fb_xrgb8888_to_mono - Convert XRGB8888 to monochrome
- * @dst: Array of monochrome destination buffers (0=black, 1=white)
- * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
- *             within @dst; can be NULL if scanlines are stored next to each other.
- * @src: Array of XRGB8888 source buffers
- * @fb: DRM framebuffer
- * @clip: Clip rectangle area to copy
- * @state: Transform and conversion state
- *
- * This function copies parts of a framebuffer to display memory and converts the
- * color format during the process. Destination and framebuffer formats must match. The
- * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
- * least as many entries as there are planes in @fb's format. Each entry stores the
- * value for the format's respective color plane at the same index.
- *
- * This function does not apply clipping on @dst (i.e. the destination is at the
- * top-left corner). The first pixel (upper left corner of the clip rectangle) will
- * be converted and copied to the first bit (LSB) in the first byte of the monochrome
- * destination buffer. If the caller requires that the first pixel in a byte must
- * be located at an x-coordinate that is a multiple of 8, then the caller must take
- * care itself of supplying a suitable clip rectangle.
- *
- * DRM doesn't have native monochrome support. Drivers can use this function for
- * monochrome devices that don't support XRGB8888 natively. Such drivers can
- * announce the commonly supported XR24 format to userspace and use this function
- * to convert to the native format.
- *
- * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
- * then the result is converted from grayscale to monochrome.
- */
-void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitch,
-			     const struct iosys_map *src, const struct drm_framebuffer *fb,
-			     const struct drm_rect *clip, struct drm_format_conv_state *state)
+static void drm_fb_xrgb8888_to_gray(u8 *dst, const unsigned int *dst_pitch,
+			     u8 *src, const struct drm_framebuffer *fb,
+			     const struct drm_rect *clip, struct drm_format_conv_state *state,
+			     u8 bpp,
+			     void (*xfrm_line)(void *dbuf, const void *sbuf, unsigned int npixels))
 {
 	static const unsigned int default_dst_pitch[DRM_FORMAT_MAX_PLANES] = {
 		0, 0, 0, 0
@@ -1313,11 +1303,10 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
 	unsigned int cpp = fb->format->cpp[0];
 	unsigned int len_src32 = linepixels * cpp;
 	struct drm_device *dev = fb->dev;
-	void *vaddr = src[0].vaddr;
 	unsigned int dst_pitch_0;
 	unsigned int y;
-	u8 *mono = dst[0].vaddr, *gray8;
 	u32 *src32;
+	u8 *gray8;
 
 	if (drm_WARN_ON(dev, fb->format->format != DRM_FORMAT_XRGB8888))
 		return;
@@ -1330,7 +1319,7 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
 	 * The mono destination buffer contains 1 bit per pixel
 	 */
 	if (!dst_pitch_0)
-		dst_pitch_0 = DIV_ROUND_UP(linepixels, 8);
+		dst_pitch_0 = DIV_ROUND_UP(linepixels, 8 / bpp);
 
 	/*
 	 * The dma memory is write-combined so reads are uncached.
@@ -1349,13 +1338,88 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
 
 	gray8 = (u8 *)src32 + len_src32;
 
-	vaddr += clip_offset(clip, fb->pitches[0], cpp);
+	src += clip_offset(clip, fb->pitches[0], cpp);
 	for (y = 0; y < lines; y++) {
-		src32 = memcpy(src32, vaddr, len_src32);
+		src32 = memcpy(src32, src, len_src32);
 		drm_fb_xrgb8888_to_gray8_line(gray8, src32, linepixels);
-		drm_fb_gray8_to_mono_line(mono, gray8, linepixels);
-		vaddr += fb->pitches[0];
-		mono += dst_pitch_0;
+		xfrm_line(dst, gray8, linepixels);
+		src += fb->pitches[0];
+		dst += dst_pitch_0;
 	}
 }
+
+/**
+ * drm_fb_xrgb8888_to_mono - Convert XRGB8888 to monochrome
+ * @dst: Array of monochrome destination buffers (0=black, 1=white)
+ * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
+ *             within @dst; can be NULL if scanlines are stored next to each other.
+ * @src: Array of XRGB8888 source buffers
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ * @state: Transform and conversion state
+ *
+ * DRM doesn't have native monochrome support. Drivers can use this function for
+ * monochrome devices that don't support XRGB8888 natively. Such drivers can
+ * announce the commonly supported XR24 format to userspace and use this function
+ * to convert to the native format.
+ *
+ * This function copies parts of a framebuffer to display memory and converts the
+ * color format during the process. Destination and framebuffer formats must match. The
+ * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
+ * least as many entries as there are planes in @fb's format. Each entry stores the
+ * value for the format's respective color plane at the same index.
+ *
+ * This function does not apply clipping on @dst (i.e. the destination is at the
+ * top-left corner). The first pixel (upper left corner of the clip rectangle) will
+ * be converted and copied to the first bit (LSB) in the first byte of the monochrome
+ * destination buffer. If the caller requires that the first pixel in a byte must
+ * be located at an x-coordinate that is a multiple of 8, then the caller must take
+ * care itself of supplying a suitable clip rectangle.
+ *
+ *
+ * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
+ * then the result is converted from grayscale to monochrome.
+ */
+
+
+void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitch,
+			     const struct iosys_map *src, const struct drm_framebuffer *fb,
+			     const struct drm_rect *clip, struct drm_format_conv_state *state)
+{
+	drm_fb_xrgb8888_to_gray(dst[0].vaddr, dst_pitch, src[0].vaddr, fb, clip, state,
+				1, drm_fb_gray8_to_mono_line);
+}
 EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono);
+
+/**
+ * drm_fb_xrgb8888_to_gray2 - Convert XRGB8888 to gray2
+ * @dst: Array of gray2 destination buffers
+ * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
+ *             within @dst; can be NULL if scanlines are stored next to each other.
+ * @src: Array of XRGB8888 source buffers
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ * @state: Transform and conversion state
+ *
+ * This function copies parts of a framebuffer to display memory and converts the
+ * color format during the process. Destination and framebuffer formats must match. The
+ * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
+ * least as many entries as there are planes in @fb's format. Each entry stores the
+ * value for the format's respective color plane at the same index.
+ *
+ * DRM doesn't have native gray2 support. Drivers can use this function for
+ * gray2 devices that don't support XRGB8888 natively. Such drivers can
+ * announce the commonly supported XR24 format to userspace and use this function
+ * to convert to the native format.
+ *
+ * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
+ * then the result is converted from grayscale to gray2.
+ */
+void drm_fb_xrgb8888_to_gray2(struct iosys_map *dst, const unsigned int *dst_pitch,
+			      const struct iosys_map *src, const struct drm_framebuffer *fb,
+			      const struct drm_rect *clip, struct drm_format_conv_state *state)
+{
+	drm_fb_xrgb8888_to_gray(dst[0].vaddr, dst_pitch, src[0].vaddr, fb, clip, state,
+				2, drm_fb_gray8_to_gray2_line);
+}
+EXPORT_SYMBOL(drm_fb_xrgb8888_to_gray2);
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index 562bc383ece4e90d96aa92b47b4f69609f825a6e..8488befafb7e0e0311f87bd2fef5011bab45065b 100644
--- a/include/drm/drm_format_helper.h
+++ b/include/drm/drm_format_helper.h
@@ -136,4 +136,8 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
 			     const struct iosys_map *src, const struct drm_framebuffer *fb,
 			     const struct drm_rect *clip, struct drm_format_conv_state *state);
 
+void drm_fb_xrgb8888_to_gray2(struct iosys_map *dst, const unsigned int *dst_pitch,
+			     const struct iosys_map *src, const struct drm_framebuffer *fb,
+			     const struct drm_rect *clip, struct drm_format_conv_state *state);
+
 #endif /* __LINUX_DRM_FORMAT_HELPER_H */

-- 
2.49.0

Hi

Am 14.07.25 um 10:04 schrieb Marcus Folkesson:
> drm_fb_xrgb8888_to_gray2() works like and share much code with
> drm_fb_xrgb8888_to_mono(), but converts XRGB8888 to
> 2bit grayscale instead.
>
> It uses drm_fb_xrgb8888_to_gray8() to convert the pixels to gray8 as an
> intermediate step before converting to gray2.

Please don't share code here.  This needs a serious rework anyway. The 
best thing for now is to add a new, separate function for _gray2().

Best regards
Thomas


>
> Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
> ---
>   drivers/gpu/drm/drm_format_helper.c | 148 ++++++++++++++++++++++++++----------
>   include/drm/drm_format_helper.h     |   4 +
>   2 files changed, 110 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index 8f3daf38ca639d3d39742c2c9fa0c54a3a9297a5..2f2171b3df609263cc9ce6809bf6144028c25380 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -1253,6 +1253,25 @@ int drm_fb_blit(struct iosys_map *dst, const unsigned int *dst_pitch, uint32_t d
>   }
>   EXPORT_SYMBOL(drm_fb_blit);
>   
> +static void drm_fb_gray8_to_gray2_line(void *dbuf, const void *sbuf, unsigned int pixels)
> +{
> +	u8 *dbuf8 = dbuf;
> +	const u8 *sbuf8 = sbuf;
> +	u8 px;
> +
> +	while (pixels) {
> +		unsigned int i, bits = min(pixels, 4U);
> +		u8 byte = 0;
> +
> +		for (i = 0; i < bits; i++, pixels--) {
> +			byte >>= 2;
> +			px = (*sbuf8++ * 3 + 127) / 255;
> +			byte |= (px &= 0x03) << 6;
> +		}
> +		*dbuf8++ = byte;
> +	}
> +}
> +
>   static void drm_fb_gray8_to_mono_line(void *dbuf, const void *sbuf, unsigned int pixels)
>   {
>   	u8 *dbuf8 = dbuf;
> @@ -1270,40 +1289,11 @@ static void drm_fb_gray8_to_mono_line(void *dbuf, const void *sbuf, unsigned int
>   	}
>   }
>   
> -/**
> - * drm_fb_xrgb8888_to_mono - Convert XRGB8888 to monochrome
> - * @dst: Array of monochrome destination buffers (0=black, 1=white)
> - * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
> - *             within @dst; can be NULL if scanlines are stored next to each other.
> - * @src: Array of XRGB8888 source buffers
> - * @fb: DRM framebuffer
> - * @clip: Clip rectangle area to copy
> - * @state: Transform and conversion state
> - *
> - * This function copies parts of a framebuffer to display memory and converts the
> - * color format during the process. Destination and framebuffer formats must match. The
> - * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
> - * least as many entries as there are planes in @fb's format. Each entry stores the
> - * value for the format's respective color plane at the same index.
> - *
> - * This function does not apply clipping on @dst (i.e. the destination is at the
> - * top-left corner). The first pixel (upper left corner of the clip rectangle) will
> - * be converted and copied to the first bit (LSB) in the first byte of the monochrome
> - * destination buffer. If the caller requires that the first pixel in a byte must
> - * be located at an x-coordinate that is a multiple of 8, then the caller must take
> - * care itself of supplying a suitable clip rectangle.
> - *
> - * DRM doesn't have native monochrome support. Drivers can use this function for
> - * monochrome devices that don't support XRGB8888 natively. Such drivers can
> - * announce the commonly supported XR24 format to userspace and use this function
> - * to convert to the native format.
> - *
> - * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
> - * then the result is converted from grayscale to monochrome.
> - */
> -void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitch,
> -			     const struct iosys_map *src, const struct drm_framebuffer *fb,
> -			     const struct drm_rect *clip, struct drm_format_conv_state *state)
> +static void drm_fb_xrgb8888_to_gray(u8 *dst, const unsigned int *dst_pitch,
> +			     u8 *src, const struct drm_framebuffer *fb,
> +			     const struct drm_rect *clip, struct drm_format_conv_state *state,
> +			     u8 bpp,
> +			     void (*xfrm_line)(void *dbuf, const void *sbuf, unsigned int npixels))
>   {
>   	static const unsigned int default_dst_pitch[DRM_FORMAT_MAX_PLANES] = {
>   		0, 0, 0, 0
> @@ -1313,11 +1303,10 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
>   	unsigned int cpp = fb->format->cpp[0];
>   	unsigned int len_src32 = linepixels * cpp;
>   	struct drm_device *dev = fb->dev;
> -	void *vaddr = src[0].vaddr;
>   	unsigned int dst_pitch_0;
>   	unsigned int y;
> -	u8 *mono = dst[0].vaddr, *gray8;
>   	u32 *src32;
> +	u8 *gray8;
>   
>   	if (drm_WARN_ON(dev, fb->format->format != DRM_FORMAT_XRGB8888))
>   		return;
> @@ -1330,7 +1319,7 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
>   	 * The mono destination buffer contains 1 bit per pixel
>   	 */
>   	if (!dst_pitch_0)
> -		dst_pitch_0 = DIV_ROUND_UP(linepixels, 8);
> +		dst_pitch_0 = DIV_ROUND_UP(linepixels, 8 / bpp);
>   
>   	/*
>   	 * The dma memory is write-combined so reads are uncached.
> @@ -1349,13 +1338,88 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
>   
>   	gray8 = (u8 *)src32 + len_src32;
>   
> -	vaddr += clip_offset(clip, fb->pitches[0], cpp);
> +	src += clip_offset(clip, fb->pitches[0], cpp);
>   	for (y = 0; y < lines; y++) {
> -		src32 = memcpy(src32, vaddr, len_src32);
> +		src32 = memcpy(src32, src, len_src32);
>   		drm_fb_xrgb8888_to_gray8_line(gray8, src32, linepixels);
> -		drm_fb_gray8_to_mono_line(mono, gray8, linepixels);
> -		vaddr += fb->pitches[0];
> -		mono += dst_pitch_0;
> +		xfrm_line(dst, gray8, linepixels);
> +		src += fb->pitches[0];
> +		dst += dst_pitch_0;
>   	}
>   }
> +
> +/**
> + * drm_fb_xrgb8888_to_mono - Convert XRGB8888 to monochrome
> + * @dst: Array of monochrome destination buffers (0=black, 1=white)
> + * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
> + *             within @dst; can be NULL if scanlines are stored next to each other.
> + * @src: Array of XRGB8888 source buffers
> + * @fb: DRM framebuffer
> + * @clip: Clip rectangle area to copy
> + * @state: Transform and conversion state
> + *
> + * DRM doesn't have native monochrome support. Drivers can use this function for
> + * monochrome devices that don't support XRGB8888 natively. Such drivers can
> + * announce the commonly supported XR24 format to userspace and use this function
> + * to convert to the native format.
> + *
> + * This function copies parts of a framebuffer to display memory and converts the
> + * color format during the process. Destination and framebuffer formats must match. The
> + * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
> + * least as many entries as there are planes in @fb's format. Each entry stores the
> + * value for the format's respective color plane at the same index.
> + *
> + * This function does not apply clipping on @dst (i.e. the destination is at the
> + * top-left corner). The first pixel (upper left corner of the clip rectangle) will
> + * be converted and copied to the first bit (LSB) in the first byte of the monochrome
> + * destination buffer. If the caller requires that the first pixel in a byte must
> + * be located at an x-coordinate that is a multiple of 8, then the caller must take
> + * care itself of supplying a suitable clip rectangle.
> + *
> + *
> + * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
> + * then the result is converted from grayscale to monochrome.
> + */
> +
> +
> +void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitch,
> +			     const struct iosys_map *src, const struct drm_framebuffer *fb,
> +			     const struct drm_rect *clip, struct drm_format_conv_state *state)
> +{
> +	drm_fb_xrgb8888_to_gray(dst[0].vaddr, dst_pitch, src[0].vaddr, fb, clip, state,
> +				1, drm_fb_gray8_to_mono_line);
> +}
>   EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono);
> +
> +/**
> + * drm_fb_xrgb8888_to_gray2 - Convert XRGB8888 to gray2
> + * @dst: Array of gray2 destination buffers
> + * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
> + *             within @dst; can be NULL if scanlines are stored next to each other.
> + * @src: Array of XRGB8888 source buffers
> + * @fb: DRM framebuffer
> + * @clip: Clip rectangle area to copy
> + * @state: Transform and conversion state
> + *
> + * This function copies parts of a framebuffer to display memory and converts the
> + * color format during the process. Destination and framebuffer formats must match. The
> + * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
> + * least as many entries as there are planes in @fb's format. Each entry stores the
> + * value for the format's respective color plane at the same index.
> + *
> + * DRM doesn't have native gray2 support. Drivers can use this function for
> + * gray2 devices that don't support XRGB8888 natively. Such drivers can
> + * announce the commonly supported XR24 format to userspace and use this function
> + * to convert to the native format.
> + *
> + * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
> + * then the result is converted from grayscale to gray2.
> + */
> +void drm_fb_xrgb8888_to_gray2(struct iosys_map *dst, const unsigned int *dst_pitch,
> +			      const struct iosys_map *src, const struct drm_framebuffer *fb,
> +			      const struct drm_rect *clip, struct drm_format_conv_state *state)
> +{
> +	drm_fb_xrgb8888_to_gray(dst[0].vaddr, dst_pitch, src[0].vaddr, fb, clip, state,
> +				2, drm_fb_gray8_to_gray2_line);
> +}
> +EXPORT_SYMBOL(drm_fb_xrgb8888_to_gray2);
> diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
> index 562bc383ece4e90d96aa92b47b4f69609f825a6e..8488befafb7e0e0311f87bd2fef5011bab45065b 100644
> --- a/include/drm/drm_format_helper.h
> +++ b/include/drm/drm_format_helper.h
> @@ -136,4 +136,8 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
>   			     const struct iosys_map *src, const struct drm_framebuffer *fb,
>   			     const struct drm_rect *clip, struct drm_format_conv_state *state);
>   
> +void drm_fb_xrgb8888_to_gray2(struct iosys_map *dst, const unsigned int *dst_pitch,
> +			     const struct iosys_map *src, const struct drm_framebuffer *fb,
> +			     const struct drm_rect *clip, struct drm_format_conv_state *state);
> +
>   #endif /* __LINUX_DRM_FORMAT_HELPER_H */
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Hi Thomas,


Thank you for your comments!

On Mon, Jul 14, 2025 at 11:13:04AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 14.07.25 um 10:04 schrieb Marcus Folkesson:
> > drm_fb_xrgb8888_to_gray2() works like and share much code with
> > drm_fb_xrgb8888_to_mono(), but converts XRGB8888 to
> > 2bit grayscale instead.
> > 
> > It uses drm_fb_xrgb8888_to_gray8() to convert the pixels to gray8 as an
> > intermediate step before converting to gray2.
> 
> Please don't share code here.  This needs a serious rework anyway. The best
> thing for now is to add a new, separate function for _gray2().

I see. I will instead add a separate _gray() function, even though it
will look very similar to _mono.

> 
> Best regards
> Thomas

Best regards,
Marcus Folkesson