Unverified Commit 7392f245 authored by Geert Uytterhoeven's avatar Geert Uytterhoeven Committed by Javier Martinez Canillas
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drm/format-helper: Fix XRGB888 to monochrome conversion 



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: bcf8b616 ("drm/format-helper: Add drm_fb_xrgb8888_to_mono_reversed()")
Signed-off-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
Acked-by: default avatarJavier Martinez Canillas <javierm@redhat.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarJavier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220317081830.1211400-3-geert@linux-m68k.org
parent 9b13a3fc

drivers/gpu/drm/drm_format_helper.c

+18 −37
Original line number Diff line number Diff line
@@ -594,27 +594,16 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for 
}

EXPORT_SYMBOL(drm_fb_blit_toio);



static void drm_fb_gray8_to_mono_line(u8 *dst, const u8 *src, unsigned int pixels,

				      unsigned int start_offset, unsigned int end_len)

{

	unsigned int xb, i;



	for (xb = 0; xb < pixels; xb++) {

		unsigned int start = 0, end = 8;

		u8 byte = 0x00;



		if (xb == 0 && start_offset)

			start = start_offset;



		if (xb == pixels - 1 && end_len)

			end = end_len;



		for (i = start; i < end; i++) {

			unsigned int x = xb * 8 + i;

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--) {

			if (*src++ >= 128)

				byte |= BIT(i);

		}

		*dst++ = byte;

	}
@@ -634,16 +623,22 @@ static void drm_fb_gray8_to_mono_line(u8 *dst, const u8 *src, unsigned int pixel 
 *

 * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and

 * then the result is converted from grayscale to monochrome.

 *

 * 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.

 */

void drm_fb_xrgb8888_to_mono(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 lines = drm_rect_height(clip);

	unsigned int cpp = fb->format->cpp[0];

	unsigned int len_src32 = linepixels * cpp;

	struct drm_device *dev = fb->dev;

	unsigned int start_offset, end_len;

	unsigned int y;

	u8 *mono = dst, *gray8;

	u32 *src32;
@@ -652,14 +647,11 @@ void drm_fb_xrgb8888_to_mono(void *dst, unsigned int dst_pitch, const void *vadd 
		return;



	/*

	 * The mono destination buffer contains 1 bit per pixel and

	 * destination scanlines have to be in multiple of 8 pixels.

	 * The mono destination buffer contains 1 bit per pixel

	 */

	if (!dst_pitch)

		dst_pitch = DIV_ROUND_UP(linepixels, 8);



	drm_WARN_ONCE(dev, dst_pitch % 8 != 0, "dst_pitch is not a multiple of 8\n");



	/*

	 * The cma memory is write-combined so reads are uncached.

	 * Speed up by fetching one line at a time.
@@ -677,22 +669,11 @@ void drm_fb_xrgb8888_to_mono(void *dst, unsigned int dst_pitch, const void *vadd 


	gray8 = (u8 *)src32 + len_src32;



	/*

	 * 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 mono line conversion function to adjust.

	 */

	start_offset = clip->x1 % 8;

	end_len = clip->x2 % 8;



	vaddr += clip_offset(clip, fb->pitches[0], cpp);

	for (y = 0; y < lines; y++) {

		src32 = memcpy(src32, vaddr, len_src32);

		drm_fb_xrgb8888_to_gray8_line(gray8, src32, linepixels);

		drm_fb_gray8_to_mono_line(mono, gray8, dst_pitch, start_offset, end_len);

		drm_fb_gray8_to_mono_line(mono, gray8, linepixels);

		vaddr += fb->pitches[0];

		mono += dst_pitch;

	}