Re: [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888,gray8}_to_mono_reversed()

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Am 04.02.22 um 16:52 schrieb Thomas Zimmermann:
[...]
+/**
+ * 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, ...);

Here, I meant 'drm_fb_gray8_to_mono_reversed_line()'


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

     kfree(tmp);
   }

To elaborate, this is an example of what I meant by composable. In the future, we can generalize this function and hand-in 2 function pointers the do the conversion with tmp as intermediate buffer. That would work for any combination of formats that have a common intermediate format.


Best regards
Thomas

+}
+EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono_reversed);
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index b30ed5de0a33..85e551a5cbe6 100644
--- a/include/drm/drm_format_helper.h
+++ b/include/drm/drm_format_helper.h
@@ -43,4 +43,11 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
               const void *vmap, const struct drm_framebuffer *fb,
               const struct drm_rect *rect);
+void drm_fb_gray8_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *src,
+                   const struct drm_rect *clip);
+
+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);
+
  #endif /* __LINUX_DRM_FORMAT_HELPER_H */


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

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