[PATCH 6.19 199/311] drm/ast: dp501: Fix initialization of SCU2C

Greg Kroah-Hartman
2026-04-08T18:58:20Z

From: Thomas Zimmermann <tzimmermann@suse.de>

commit 2f42c1a6161646cbd29b443459fd635d29eda634 upstream.

Ast's DP501 initialization reads the register SCU2C at offset 0x1202c
and tries to set it to source data from VGA. But writes the update to
offset 0x0, with unknown results. Write the result to SCU instead.

The bug only happens in ast_init_analog(). There's similar code in
ast_init_dvo(), which works correctly.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 83c6620bae3f ("drm/ast: initial DP501 support (v0.2)")
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v3.16+
Link: https://patch.msgid.link/20260327133532.79696-2-tzimmermann@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/ast/ast_dp501.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/ast/ast_dp501.c
+++ b/drivers/gpu/drm/ast/ast_dp501.c
@@ -436,7 +436,7 @@ static void ast_init_analog(struct ast_d
/* Finally, clear bits [17:16] of SCU2c */
data = ast_read32(ast, 0x1202c);
data &= 0xfffcffff;
- ast_write32(ast, 0, data);
+ ast_write32(ast, 0x1202c, data);

/* Disable DVO */
ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xa3, 0xcf, 0x00);