On 3/15/22 12:07, Geert Uytterhoeven wrote:
The conversion functions drm_fb_xrgb8888_to_mono() and drm_fb_gray8_to_mono_line() do not behave correctly when the horizontal boundaries of the clip rectangle are not multiples of 8: a. When x1 % 8 != 0, the calculated pitch is not correct, b. When x2 % 8 != 0, the pixel data for the last byte is wrong.
Thanks a lot for tracking down and fixing these issues.
Simplify the code and fix (a) by:
- Removing start_offset, and always storing the first pixel in the first bit of the monochrome destination buffer. Drivers that require the first pixel in a byte to be located at an x-coordinate that is a multiple of 8 can always align the clip rectangle before calling drm_fb_xrgb8888_to_mono(). Note that:
- The ssd130x driver does not need the alignment, as the
monochrome buffer is a temporary format, - The repaper driver always updates the full screen, so the clip rectangle is always aligned.
- Passing the number of pixels to drm_fb_gray8_to_mono_line(), instead of the number of bytes, and the number of pixels in the last byte.
Fix (b) by explicitly setting the target bit, instead of always setting bit 7 and shifting the value in each loop iteration.
Remove the bogus pitch check, which operates on bytes instead of pixels, and triggers when e.g. flashing the cursor on a text console with a font that is 8 pixels wide.
Drop the confusing comment about scanlines, as a pitch in bytes always contains a multiple of 8 pixels.
While at it, use the drm_rect_height() helper instead of open-coding the same operation.
Update the comments accordingly.
Fixes: bcf8b616deb87941 ("drm/format-helper: Add drm_fb_xrgb8888_to_mono_reversed()") Signed-off-by: Geert Uytterhoeven geert@linux-m68k.org
Acked-by: Javier Martinez Canillas javierm@redhat.com
I just have a small comment below.
[snip]
+static void drm_fb_gray8_to_mono_line(u8 *dst, const u8 *src, unsigned int pixels) +{
- while (pixels) {
unsigned int i, bits = min(pixels, 8U);u8 byte = 0;
byte >>= 1;if (src[x] >> 7)byte |= BIT(7);
for (i = 0; i < bits; i++, pixels--) {
I think is worth to add a comment here explaining that the pixel is set to 1 for brightness > 127 and to 0 for brightness < 128. Or as kernel-doc for this helper function.
if (*src++ & BIT(7))
Pekka also mentioned that if (*src++ > 127) would make this easier to read.
byte |= BIT(i);