Patch "drm/ast: dp501: Fix initialization of SCU2C" has been added to the 5.10-stable tree

Patch "drm/ast: dp501: Fix initialization of SCU2C" has been added to the 5.10-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    drm/ast: dp501: Fix initialization of SCU2C

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-ast-dp501-fix-initialization-of-scu2c.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From 2f42c1a6161646cbd29b443459fd635d29eda634 Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann@suse.de>
Date: Fri, 27 Mar 2026 14:32:53 +0100
Subject: drm/ast: dp501: Fix initialization of SCU2C

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
@@ -484,7 +484,7 @@ static void ast_init_analog(struct drm_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_CRTC_PORT, 0xa3, 0xcf, 0x00);


Patches currently in stable-queue which might be from tzimmermann@suse.de are

queue-5.10/drm-ioc32-stop-speculation-on-the-drm_compat_ioctl-path.patch
queue-5.10/drm-ast-dp501-fix-initialization-of-scu2c.patch