Hi

Am 04.02.22 um 20:31 schrieb Javier Martinez Canillas:

Hello Thomas,

Thanks a lot for your feedback.

On 2/4/22 16:52, Thomas Zimmermann wrote:

[snip]

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+static void drm_fb_gray8_to_mono_reversed_line(u8 *dst, const u8 *src, size_t pixels)
+{
+	unsigned int xb, i;
+
+	for (xb = 0; xb < pixels / 8; xb++) {

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)

Agreed.

After sending the mail, I realized that some code copies only parts of 
the source around; specifically for damage handling. None of this is 
aligned to multiple of 8. So the copying could start and end in the 
middle of bytes. You'd need a pixel-offset value of some sort.

If you don't want to handle this now, maybe at least detect this case 
and put a warning somewhere.

  
[snip]

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+ * 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.

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+{
+
+	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).

Ok.
  

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+
+	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.

Yes, I know but for reversed mono we want only 1/8 of the width since we
are converting from 8 bits per pixel greyscale to 1 bit per pixel mono.

Or am I misunderstanding what you meant ?

I mean that if there are 80 pixel on a scanline, the value of dst_pitch 
is already 10. These pitch values are always given in bytes.

Best regards
Thomas

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+		gray8 += dst_pitch;

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

Ok.
  
[snip]

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+ */
+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);
    }

I see. Yes, that sounds a much better approach. I'll change it in v3.
  
Best regards,

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