On 24/10/2025 09:35, Thomas Zimmermann wrote:

Preserve the I/O register bits in __ast_write8_i_masked() as specified by preserve_mask. Accidentally OR-ing the output value into these will overwrite the register's previous settings.

Fixes display output on the AST2300, where the screen can go blank at boot. The driver's original commit 312fec1405dd ("drm: Initial KMS driver for AST (ASpeed Technologies) 2000 series (v2)") already added the broken code. Commit 6f719373b943 ("drm/ast: Blank with VGACR17 sync enable, always clear VGACRB6 sync off") triggered the bug.

Thanks, it looks good to me.

Reviewed-by: Jocelyn Falempe jfalempe@redhat.com>

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@googl... 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)