 code. Commit 6f719373b943 ("drm/ast: Blank with VGACR17 sync
enable, always clear VGACRB6 sync off") triggered the bug.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reported-by: Peter Schneider <pschneider1968@googlemail.com>
Closes: https://lore.kernel.org/dri-devel/a40caf8e-58ad-4f9c-af7f-54f6f69c29bb@googlemail.com/
Tested-by: Peter Schneider <pschneider1968@googlemail.com>
Fixes: 6f719373b943 ("drm/ast: Blank with VGACR17 sync enable, always clear VGACRB6 sync off")
Fixes: 312fec1405dd ("drm: Initial KMS driver for AST (ASpeed Technologies) 2000 series (v2)")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Nick Bowler <nbowler@draconx.ca>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v3.5+
---
 drivers/gpu/drm/ast/ast_drv.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_drv.h b/drivers/gpu/drm/ast/ast_drv.h
index 7be36a358e74..787e38c6c17d 100644
--- a/drivers/gpu/drm/ast/ast_drv.h
+++ b/drivers/gpu/drm/ast/ast_drv.h
@@ -298,13 +298,13 @@ static inline void __ast_write8_i(void __iomem *addr, u32 reg, u8 index, u8 val)
 	__ast_write8(addr, reg + 1, val);
 }
 
-static inline void __ast_write8_i_masked(void __iomem *addr, u32 reg, u8 index, u8 read_mask,
+static inline void __ast_write8_i_masked(void __iomem *addr, u32 reg, u8 index, u8 preserve_mask,
 					 u8 val)
 {
-	u8 tmp = __ast_read8_i_masked(addr, reg, index, read_mask);
+	u8 tmp = __ast_read8_i_masked(addr, reg, index, preserve_mask);
 
-	tmp |= val;
-	__ast_write8_i(addr, reg, index, tmp);
+	val &= ~preserve_mask;
+	__ast_write8_i(addr, reg, index, tmp | val);
 }
 
 static inline u32 ast_read32(struct ast_device *ast, u32 reg)
-- 
2.51.0[PATCH] drm/ast: Clear preserved bits from register output valueThomas Zimmermann <tzimmermann@suse.de> undefinedairlied@redhat.com, jfalempe@redhat.com, pschneider1968@googlemail.com, airlied@gmail.com, simona@ffwll.ch undefined undefined undefined undefined undefined undefined undefined undefined undefined±