Commit a9fb41b5 authored by Thomas Zimmermann's avatar Thomas Zimmermann
Browse files

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 312fec14 ("drm: Initial KMS
driver for AST (ASpeed Technologies) 2000 series (v2)") already added
the broken code. Commit 6f719373 ("drm/ast: Blank with VGACR17 sync
enable, always clear VGACRB6 sync off") triggered the bug.

Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Reported-by: default avatarPeter Schneider <pschneider1968@googlemail.com>
Closes: https://lore.kernel.org/dri-devel/a40caf8e-58ad-4f9c-af7f-54f6f69c29bb@googlemail.com/


Tested-by: default avatarPeter Schneider <pschneider1968@googlemail.com>
Reviewed-by: default avatarJocelyn Falempe <jfalempe@redhat.com>
Fixes: 6f719373 ("drm/ast: Blank with VGACR17 sync enable, always clear VGACRB6 sync off")
Fixes: 312fec14 ("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+
Link: https://patch.msgid.link/20251024073626.129032-1-tzimmermann@suse.de
parent bf7e9791

drivers/gpu/drm/ast/ast_drv.h

+4 −4
Original line number Diff line number Diff line
@@ -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)