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7392f2459e
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.
Simplify the code and fix (a) by:
1. 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.
2. 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: bcf8b616de ("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>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220317081830.1211400-3-geert@linux-m68k.org
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