Hi

Am 09.02.22 um 10:03 schrieb Javier Martinez Canillas:

end_offset should be called end_len, because it is the number of bits in
the final byte; but not the offset of the final bit.

+
+		for (i = start; i < end; i++) {
+			unsigned int x = xb * 8 + i;
+
+			byte >>= 1;
+			if (src[x] >> 7)
+				byte |= BIT(7);
+		}
+		*dst++ = byte;
+	}
+}
+
+/**
+ * drm_fb_gray8_to_mono_reversed - Convert grayscale to reversed monochrome
+ * @dst: reversed monochrome destination buffer
+ * @dst_pitch: Number of bytes between two consecutive scanlines within dst
+ * @src: 8-bit grayscale source buffer
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ *
+ * DRM doesn't have native monochrome or grayscale support.
+ * Such drivers can announce the commonly supported XR24 format to userspace
+ * and use drm_fb_xrgb8888_to_gray8() to convert to grayscale and then this
+ * helper function to convert to the native format.
+ */
+void drm_fb_gray8_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *vaddr,
+				   const struct drm_framebuffer *fb,
+				   const struct drm_rect *clip)
+{
+
+	unsigned int linepixels = drm_rect_width(clip);
+	unsigned int lines = drm_rect_height(clip);
+	unsigned int start_offset, end_offset;
+	unsigned int y;
+	const u8 *gray8 = vaddr;
+	u8 *mono = dst;
+
+	/*
+	 * The reversed mono destination buffer contains 1 bit per pixel
+	 * and destination scanlines have to be in multiple of 8 pixels.
+	 */
+	if (!dst_pitch)
+		dst_pitch = DIV_ROUND_UP(linepixels, 8);
+
+	/*
+	 * For damage handling, it is possible that only parts of the source
+	 * buffer is copied and this could lead to start and end pixels that
+	 * are not aligned to multiple of 8.
+	 *
+	 * Calculate if the start and end pixels are not aligned and set the
+	 * offsets for the reversed mono line conversion function to adjust.
+	 */
+	start_offset = clip->x1 % 8;
+	end_offset = clip->x2 % 8;
+
+	for (y = 0; y < lines; y++) {
+		drm_fb_gray8_to_mono_reversed_line(mono, gray8, dst_pitch,
+						   start_offset, end_offset);
+		gray8 += fb->pitches[0];
+		mono += dst_pitch;
+	}
+}

Do you really need that function. It's not exported and if it's not 
otherwise used, I'd just remove it.  We don't keep unused interfaces around.

+
+/**
+ * drm_fb_xrgb8888_to_mono_reversed - Convert XRGB8888 to reversed monochrome
+ * @dst: reversed monochrome destination buffer
+ * @dst_pitch: Number of bytes between two consecutive scanlines within dst
+ * @src: XRGB8888 source buffer
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ *
+ * DRM doesn't have native monochrome support.
+ * 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 reversed monohrome.
+ */
+void drm_fb_xrgb8888_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *vaddr,
+				      const struct drm_framebuffer *fb, const struct drm_rect *clip)
+{
+	unsigned int linepixels = drm_rect_width(clip);
+	unsigned int lines = clip->y2 - clip->y1;
+	unsigned int cpp = fb->format->cpp[0];
+	unsigned int len_src32 = linepixels * cpp;
+	unsigned int start_offset, end_offset;
+	unsigned int y;
+	u8 *mono = dst, *gray8;
+	u32 *src32;
+
+	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
+		return;
+
+	/*
+	 * The reversed mono destination buffer contains 1 bit per pixel
+	 * and destination scanlines have to be in multiple of 8 pixels.
+	 */
+	if (!dst_pitch)
+		dst_pitch = DIV_ROUND_UP(linepixels, 8);

I'd do a warn_once if (dst_pitch % 8 != 0).

+
+	/*
+	 * The cma memory is write-combined so reads are uncached.
+	 * Speed up by fetching one line at a time.

I once had a patchset that adds caching information to struct 
dma_buf_map (soon to be named struct iosys_map).  Blitting helpers would 
be able to enable/disable this optimization as needed.

However, your driver doesn't use CMA. It's backed by SHMEM. Do you 
really want to keep that code in?

+	 */
+	src32 = kmalloc(len_src32, GFP_KERNEL);
+	if (!src32)
+		return;
+
+	/*
+	 * Copies are done line-by-line, allocate an intermediate
+	 * buffer to copy the gray8 lines and then convert to mono.
+	 */
+	gray8 = kmalloc(linepixels, GFP_KERNEL);
+	if (!gray8)
+		goto free_src32;

If might be faster to allocate both buffers in one step and set the 
pointers into the allocated buffer.

+
+	/*
+	 * For damage handling, it is possible that only parts of the source
+	 * buffer is copied and this could lead to start and end pixels that
+	 * are not aligned to multiple of 8.
+	 *
+	 * Calculate if the start and end pixels are not aligned and set the
+	 * offsets for the reversed mono line conversion function to adjust.
+	 */
+	start_offset = clip->x1 % 8;
+	end_offset = clip->x2 % 8;

end_len, again. If you have 1 single bit set in the final byte, the
offset is 0, but the length is 1.

Best regards
Thomas

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev