drm/format-helper: Store RGB565 in little-endian order

Fix to-RGB565 conversion helpers to store the result in little-
endian byte order. Update test cases as well.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: José Expósito <jose.exposito89@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230102112927.26565-5-tzimmermann@suse.de

drivers/gpu/drm/drm_format_helper.c

@@ -322,7 +322,7 @@ EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb332);
 
 static void drm_fb_xrgb8888_to_rgb565_line(void *dbuf, const void *sbuf, unsigned int pixels)
 {
-	u16 *dbuf16 = dbuf;
+	__le16 *dbuf16 = dbuf;
 	const __le32 *sbuf32 = sbuf;
 	unsigned int x;
 	u16 val16;
@@ -333,14 +333,15 @@ static void drm_fb_xrgb8888_to_rgb565_line(void *dbuf, const void *sbuf, unsigne
 		val16 = ((pix & 0x00F80000) >> 8) |
 			((pix & 0x0000FC00) >> 5) |
 			((pix & 0x000000F8) >> 3);
-		dbuf16[x] = val16;
+		dbuf16[x] = cpu_to_le16(val16);
 	}
 }
 
+/* TODO: implement this helper as conversion to RGB565|BIG_ENDIAN */
 static void drm_fb_xrgb8888_to_rgb565_swab_line(void *dbuf, const void *sbuf,
 						unsigned int pixels)
 {
-	u16 *dbuf16 = dbuf;
+	__le16 *dbuf16 = dbuf;
 	const __le32 *sbuf32 = sbuf;
 	unsigned int x;
 	u16 val16;
@@ -351,7 +352,7 @@ static void drm_fb_xrgb8888_to_rgb565_swab_line(void *dbuf, const void *sbuf,
 		val16 = ((pix & 0x00F80000) >> 8) |
 			((pix & 0x0000FC00) >> 5) |
 			((pix & 0x000000F8) >> 3);
-		dbuf16[x] = swab16(val16);
+		dbuf16[x] = cpu_to_le16(swab16(val16));
 	}
 }
 

drivers/gpu/drm/tests/drm_format_helper_test.c

@@ -264,6 +264,21 @@ static size_t conversion_buf_size(u32 dst_format, unsigned int dst_pitch,
 	return dst_pitch * drm_rect_height(clip);
 }
 
+static u16 *le16buf_to_cpu(struct kunit *test, const __le16 *buf, size_t buf_size)
+{
+	u16 *dst = NULL;
+	int n;
+
+	dst = kunit_kzalloc(test, sizeof(*dst) * buf_size, GFP_KERNEL);
+	if (!dst)
+		return NULL;
+
+	for (n = 0; n < buf_size; n++)
+		dst[n] = le16_to_cpu(buf[n]);
+
+	return dst;
+}
+
 static u32 *le32buf_to_cpu(struct kunit *test, const u32 *buf, size_t buf_size)
 {
 	u32 *dst = NULL;
@@ -368,7 +383,7 @@ static void drm_test_fb_xrgb8888_to_rgb565(struct kunit *test)
 	const struct convert_xrgb8888_case *params = test->param_value;
 	const struct convert_to_rgb565_result *result = &params->rgb565_result;
 	size_t dst_size;
-	__u16 *buf = NULL;
+	u16 *buf = NULL;
 	__le32 *xrgb8888 = NULL;
 	struct iosys_map dst, src;
 
@@ -390,9 +405,12 @@ static void drm_test_fb_xrgb8888_to_rgb565(struct kunit *test)
 	iosys_map_set_vaddr(&src, xrgb8888);
 
 	drm_fb_xrgb8888_to_rgb565(&dst, &result->dst_pitch, &src, &fb, &params->clip, false);
+	buf = le16buf_to_cpu(test, (__force const __le16 *)buf, dst_size / sizeof(__le16));
 	KUNIT_EXPECT_EQ(test, memcmp(buf, result->expected, dst_size), 0);
 
+	buf = dst.vaddr; /* restore original value of buf */
 	drm_fb_xrgb8888_to_rgb565(&dst, &result->dst_pitch, &src, &fb, &params->clip, true);
+	buf = le16buf_to_cpu(test, (__force const __le16 *)buf, dst_size / sizeof(__le16));
 	KUNIT_EXPECT_EQ(test, memcmp(buf, result->expected_swab, dst_size), 0);
 }