diff --git a/drivers/gpu/drm/radeon/radeon_atombios.c b/drivers/gpu/drm/radeon/radeon_atombios.c
index fecd705a1a5f4fa66b0bfe6e0abade805040173b..933a2cd7bb5583820b45d9b37b5820468b97923a 100644
--- a/drivers/gpu/drm/radeon/radeon_atombios.c
+++ b/drivers/gpu/drm/radeon/radeon_atombios.c
@@ -181,6 +181,18 @@ void radeon_atombios_i2c_init(struct radeon_device *rdev)
 			gpio = &i2c_info->asGPIO_Info[i];
 			i2c.valid = false;
 
+			/* 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) &&