Hi

Am 04.02.22 um 14:43 schrieb Javier Martinez Canillas:

In practice, all mode widths are multiples of 8 because VGA mandated it. 
So it's ok-ish to assume this here. You should probably at least print a 
warning somewhere if (pixels % 8 != 0)

+		u8 byte = 0x00;
+
+		for (i = 0; i < 8; i++) {
+			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
+ * @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 *src,
+				   const struct drm_rect *clip)

There's a bug here. You want to pass in a drm_framebuffer as fourth 
argument.

+{
+
+	size_t height = drm_rect_height(clip);
+	size_t width = drm_rect_width(clip);
+	unsigned int y;
+	const u8 *gray8 = src;
+	u8 *mono = dst;
+
+	if (!dst_pitch)
+		dst_pitch = width;

The dst_pitch is given in bytes. You have to device by 8. Here would be 
a good place to warn if (width % 8 != 0).

+
+	for (y = 0; y < height; y++) {
+		drm_fb_gray8_to_mono_reversed_line(mono, gray8, dst_pitch);
+		mono += (dst_pitch / 8);

The dst_pitch is already given in bytes.

+		gray8 += dst_pitch;

'gray8 += fb->pitches[0]' would be correct.

+	}
+}
+
+/**
+ * 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 *src,
+				      const struct drm_framebuffer *fb,
+				      const struct drm_rect *clip)
+{
+	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
+		return;
+
+	if (!dst_pitch)
+		dst_pitch = drm_rect_width(clip);
+
+	drm_fb_xrgb8888_to_gray8(dst, dst_pitch, src, fb, clip);
+	drm_fb_gray8_to_mono_reversed(dst, dst_pitch, dst, fb, clip);

Converting from dst into dst can give incorrect results. At some point 
we probably want to add restrict qualifiers to these pointers, to help 
the compiler with optimizing.

A better approach here is to pull the per-line conversion from 
drm_fb_xrgb8888_to_gray8() into a separate helper and implement a 
line-by-line conversion here. something like this:

   drm_fb_xrgb8888_to_mono_reversed()
   {
     char *tmp = kmalloc(size of a single line of gray8)

     for (heigth) {
        drm_fb_xrgb8888_to_gray8_line(tmp, ..., src, ...);
        drm_fb_gray8_to_mono_reversed(dst, ..., tmp, ...);

        src += fb->pitches[0]
        dst += dst_pitch;
     }

     kfree(tmp);
   }

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