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.
Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
---
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)
+{
+ 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++) {
+ u8 byte = 0x00;
+
+ for (i = 0; i < 8; i++) {
+ int x = xb * 8 + i;
+
+ byte >>= 1;
+ if (gray8[y * width + x] >> 7)
+ byte |= BIT(7);
+ }
+ *mono++ = byte;
+ }
+}
+EXPORT_SYMBOL(drm_fb_gray8_to_mono_reversed);
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index b30ed5de0a33..cd4c8b7c78de 100644
--- a/include/drm/drm_format_helper.h
+++ b/include/drm/drm_format_helper.h
@@ -43,4 +43,6 @@ 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, void *vaddr, const struct drm_rect *clip);
+
#endif /* __LINUX_DRM_FORMAT_HELPER_H */
--
2.34.1
