drm/radeon/kms: fix s/r issues with bios scratch regs

The accelerate mode bit gets checked by certain atom
command tables to set up some register state.  It needs
to be clear when setting modes and set when not.

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=26942

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon_atombios.c b/drivers/gpu/drm/radeon/radeon_atombios.c
index 4dc9c51..b64e603 100644
--- a/drivers/gpu/drm/radeon/radeon_atombios.c
+++ b/drivers/gpu/drm/radeon/radeon_atombios.c
@@ -2609,7 +2609,7 @@
 	bios_2_scratch &= ~ATOM_S2_VRI_BRIGHT_ENABLE;
 
 	/* tell the bios not to handle mode switching */
-	bios_6_scratch |= (ATOM_S6_ACC_BLOCK_DISPLAY_SWITCH | ATOM_S6_ACC_MODE);
+	bios_6_scratch |= ATOM_S6_ACC_BLOCK_DISPLAY_SWITCH;
 
 	if (rdev->family >= CHIP_R600) {
 		WREG32(R600_BIOS_2_SCRATCH, bios_2_scratch);
@@ -2660,10 +2660,13 @@
 	else
 		bios_6_scratch = RREG32(RADEON_BIOS_6_SCRATCH);
 
-	if (lock)
+	if (lock) {
 		bios_6_scratch |= ATOM_S6_CRITICAL_STATE;
-	else
+		bios_6_scratch &= ~ATOM_S6_ACC_MODE;
+	} else {
 		bios_6_scratch &= ~ATOM_S6_CRITICAL_STATE;
+		bios_6_scratch |= ATOM_S6_ACC_MODE;
+	}
 
 	if (rdev->family >= CHIP_R600)
 		WREG32(R600_BIOS_6_SCRATCH, bios_6_scratch);