From: Thomas Zimmermann Date: Fri, 24 Oct 2025 07:35:53 +0000 (+0200) Subject: drm/ast: Clear preserved bits from register output value X-Git-Tag: v6.18-rc4~10^2~1^2 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a9fb41b5def8e1e0103d5fd1453787993587281e;p=thirdparty%2Fkernel%2Fstable.git drm/ast: Clear preserved bits from register output value 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. Signed-off-by: Thomas Zimmermann Reported-by: Peter Schneider Closes: https://lore.kernel.org/dri-devel/a40caf8e-58ad-4f9c-af7f-54f6f69c29bb@googlemail.com/ Tested-by: Peter Schneider Reviewed-by: Jocelyn Falempe 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 Cc: Nick Bowler Cc: Douglas Anderson Cc: Dave Airlie Cc: Jocelyn Falempe Cc: dri-devel@lists.freedesktop.org Cc: # v3.5+ Link: https://patch.msgid.link/20251024073626.129032-1-tzimmermann@suse.de --- diff --git a/drivers/gpu/drm/ast/ast_drv.h b/drivers/gpu/drm/ast/ast_drv.h index c15aef014f69..d41bd876167c 100644 --- a/drivers/gpu/drm/ast/ast_drv.h +++ b/drivers/gpu/drm/ast/ast_drv.h @@ -282,13 +282,13 @@ 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)