[PATCH v3 02/13] drm/format-helper: Comment on RGB888 byte order

[Thomas Zimmermann]

RGB888 is different than the other formats as most of its pixels are
unaligned and therefore helper functions do not use endianness conversion
helpers. Comment on this in the source code.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Reviewed-by: Maíra Canal <mcanal at igalia.com>
Reviewed-by: José Expósito <jose.exposito89 at gmail.com>
---
 drivers/gpu/drm/drm_format_helper.c            | 1 +
 drivers/gpu/drm/tests/drm_format_helper_test.c | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 74ff33c2ddaa..b98bd7c5caee 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -404,6 +404,7 @@ static void drm_fb_xrgb8888_to_rgb888_line(void *dbuf, const void *sbuf, unsigne
 
 	for (x = 0; x < pixels; x++) {
 		pix = le32_to_cpu(sbuf32[x]);
+		/* write blue-green-red to output in little endianness */
 		*dbuf8++ = (pix & 0x000000FF) >>  0;
 		*dbuf8++ = (pix & 0x0000FF00) >>  8;
 		*dbuf8++ = (pix & 0x00FF0000) >> 16;
diff --git a/drivers/gpu/drm/tests/drm_format_helper_test.c b/drivers/gpu/drm/tests/drm_format_helper_test.c
index 2191e57f2297..cd1d7da3483c 100644
--- a/drivers/gpu/drm/tests/drm_format_helper_test.c
+++ b/drivers/gpu/drm/tests/drm_format_helper_test.c
@@ -407,6 +407,10 @@ static void drm_test_fb_xrgb8888_to_rgb888(struct kunit *test)
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, xrgb8888);
 	iosys_map_set_vaddr(&src, xrgb8888);
 
+	/*
+	 * RGB888 expected results are already in little-endian
+	 * order, so there's no need to convert the test output.
+	 */
 	drm_fb_xrgb8888_to_rgb888(&dst, &result->dst_pitch, &src, &fb, &params->clip);
 	KUNIT_EXPECT_EQ(test, memcmp(buf, result->expected, dst_size), 0);
 }
-- 
2.39.0