Swap the pixel data when writing to framebuffer memory on big-endian
machines. Fixes incorrect output. Aspeed graphics does not appear to
support big-endian framebuffers after AST2400, although the feature
has been documented.

There's a lengthy discussion at [1].

Signed-off-by: René Rebe <rene@exactco.de>
Link: https://lore.kernel.org/dri-devel/20251202.170626.2134482663677806825.rene@exactco.de/ # [1]
---
The ARGB4444 cursor not yet 100% correct, but that might be another layer/helper bug.
Tested on sparc64 T4-1 running T2/Linux.
---
 drivers/gpu/drm/ast/ast_cursor.c | 11 ++++++++---
 drivers/gpu/drm/ast/ast_mode.c   | 11 +++++++++--
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_cursor.c b/drivers/gpu/drm/ast/ast_cursor.c
index 2d3ad7610c2e..d4620171d845 100644
--- a/drivers/gpu/drm/ast/ast_cursor.c
+++ b/drivers/gpu/drm/ast/ast_cursor.c
@@ -92,12 +92,17 @@ static void ast_set_cursor_image(struct ast_device *ast, const u8 *src,
 				 unsigned int width, unsigned int height)
 {
 	u8 __iomem *dst = ast_plane_vaddr(&ast->cursor_plane.base);
-	u32 csum;
-
-	csum = ast_cursor_calculate_checksum(src, width, height);
+	u32 csum = ast_cursor_calculate_checksum(src, width, height);
 
 	/* write pixel data */
+#if defined(__BIG_ENDIAN)
+	unsigned int i;
+
+	for (i = 0; i < AST_HWC_SIZE; i += 2)
+		writew(swab16(*(const __be16 *)&src[i]), &dst[i]);
+#else
 	memcpy_toio(dst, src, AST_HWC_SIZE);
+#endif
 
 	/* write checksum + signature */
 	dst += AST_HWC_SIZE;
diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index cd08990a10f9..57c6fbc3232b 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -526,12 +526,18 @@ static int ast_primary_plane_helper_atomic_check(struct drm_plane *plane,
 
 static void ast_handle_damage(struct ast_plane *ast_plane, struct iosys_map *src,
 			      struct drm_framebuffer *fb,
-			      const struct drm_rect *clip)
+			      const struct drm_rect *clip,
+			      struct drm_format_conv_state *fmtcnv_state)
 {
 	struct iosys_map dst = IOSYS_MAP_INIT_VADDR_IOMEM(ast_plane_vaddr(ast_plane));
 
 	iosys_map_incr(&dst, drm_fb_clip_offset(fb->pitches[0], fb->format, clip));
+
+#if defined(__BIG_ENDIAN)
+	drm_fb_swab(&dst, fb->pitches, src, fb, clip, !src[0].is_iomem, fmtcnv_state);
+#else
 	drm_fb_memcpy(&dst, fb->pitches, src, fb, clip);
+#endif
 }
 
 static void ast_primary_plane_helper_atomic_update(struct drm_plane *plane,
@@ -561,7 +567,8 @@ static void ast_primary_plane_helper_atomic_update(struct drm_plane *plane,
 	if (drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE) == 0) {
 		drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
 		drm_atomic_for_each_plane_damage(&iter, &damage) {
-			ast_handle_damage(ast_plane, shadow_plane_state->data, fb, &damage);
+			ast_handle_damage(ast_plane, shadow_plane_state->data, fb, &damage,
+					  &shadow_plane_state->fmtcnv_state);
 		}
 
 		drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
-- 
2.52.0

-- 
René Rebe, ExactCODE GmbH, Berlin, Germany
https://exactco.de • https://t2linux.com • https://patreon.com/renerebe