Hello Thomas,

Thanks a lot for your feedback.

On 2/1/22 10:59, Thomas Zimmermann wrote:

Hi

Am 31.01.22 um 21:12 schrieb Javier Martinez Canillas:

quoted

Add support to convert 8-bit grayscale to reversed monochrome for drivers
that control monochromatic displays, that only have 1 bit per pixel depth.

This helper function was based on repaper_gray8_to_mono_reversed() from
the drivers/gpu/drm/tiny/repaper.c driver.

You could convert repaper to the new helper.

Yes, I plan to do it but was out of scope for this patch series.

quoted

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

  drivers/gpu/drm/drm_format_helper.c | 35 +++++++++++++++++++++++++++++
  include/drm/drm_format_helper.h     |  2 ++
  2 files changed, 37 insertions(+)

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 0f28dd2bdd72..bf477c136082 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c

@@ -584,3 +584,38 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
  	return -EINVAL;
  }
  EXPORT_SYMBOL(drm_fb_blit_toio);
+
+/**
+ * drm_fb_gray8_to_mono_reversed - Convert grayscale to reversed monochrome
+ * @dst: reversed monochrome destination buffer
+ * @src: 8-bit grayscale source buffer
+ * @clip: Clip rectangle area to copy
+ *
+ * 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, void *src, const struct drm_rect *clip)

IMHO it would be better to have a function that converts xrgb8888 to 
mono and let it handle the intermediate step of gray8.

That's a good idea. I'll add that too.

quoted

+{
+	size_t width = drm_rect_width(clip);
+	size_t height = drm_rect_width(clip);
+
+	u8 *mono = dst, *gray8 = src;
+	unsigned int y, xb, i;
+
+	for (y = 0; y < height; y++)
+		for (xb = 0; xb < width / 8; xb++) {

The inner loop should probably go into a separate helper function. See 
the drm_fb_*_line() helpers in this file

At some point, we's want to have a single blit helper that takes source 
and destination formats/buffers. It would then pick the correct per-line 
helper for the conversion. So yeah, we'd want something composable.

Agreed. I'll split that into a separate helper function.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat