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>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -2609,7 +2609,7 @@ void radeon_atom_initialize_bios_scratch_regs(struct drm_device *dev)
 	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 @@ void radeon_atom_output_lock(struct drm_encoder *encoder, bool lock)
 	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);