drm/radeon/kms: fix up gpio i2c mask bits for r4xx

Fixes i2c test failures when i2c_algo_bit.bit_test=1.

The hw doesn't actually require a mask, so just set it
to the default mask bits for r1xx-r4xx radeon ddc.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@kernel.org
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -85,6 +85,18 @@ static struct radeon_i2c_bus_rec radeon_lookup_i2c_gpio(struct radeon_device *rd
 		for (i = 0; i < num_indices; i++) {
 			gpio = &i2c_info->asGPIO_Info[i];
 
+			/* r4xx mask is technically not used by the hw, so patch in the legacy mask bits */
+			if ((rdev->family == CHIP_R420) ||
+			    (rdev->family == CHIP_R423) ||
+			    (rdev->family == CHIP_RV410)) {
+				if ((le16_to_cpu(gpio->usClkMaskRegisterIndex) == 0x0018) ||
+				    (le16_to_cpu(gpio->usClkMaskRegisterIndex) == 0x0019) ||
+				    (le16_to_cpu(gpio->usClkMaskRegisterIndex) == 0x001a)) {
+					gpio->ucClkMaskShift = 0x19;
+					gpio->ucDataMaskShift = 0x18;
+				}
+			}
+
 			/* some evergreen boards have bad data for this entry */
 			if (ASIC_IS_DCE4(rdev)) {
 				if ((i == 7) &&