On Fri, Feb 4, 2022 at 10:53 AM Thomas Zimmermann [off-list ref] wrote:

Hi

Am 04.02.22 um 14:43 schrieb Javier Martinez Canillas:

quoted

Add support to convert XR24 and 8-bit grayscale to reversed monochrome for
drivers that control monochromatic panels, that only have 1 bit per pixel.

The drm_fb_gray8_to_mono_reversed() helper was based on the function that
does the same in the drivers/gpu/drm/tiny/repaper.c driver.

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

(no changes since v1)

  drivers/gpu/drm/drm_format_helper.c | 80 +++++++++++++++++++++++++++++
  include/drm/drm_format_helper.h     |  7 +++
  2 files changed, 87 insertions(+)

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 0f28dd2bdd72..cdce4b7c25d9 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c

@@ -584,3 +584,83 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
      return -EINVAL;
  }
  EXPORT_SYMBOL(drm_fb_blit_toio);
+
+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)

Not sure if it's relevant, but 1366x768 was a fairly popular laptop
resolution. There's even a dedicated drm_mode_fixup_1366x768 in
drm_edid.c. (Would it have killed them to add 2 more horizontal
pixels? Apparently.)

Cheers,

  -ilia