drm/radeon/kms: fix i2c pad masks on rs4xx

These got lost in the last i2c cleanup.  Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=23222

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_combios.c

@@ -571,6 +571,7 @@ static struct radeon_i2c_bus_rec combios_setup_i2c_bus(struct radeon_device *rde
 	}
 
 	if (clk_mask && data_mask) {
+		/* system specific masks */
 		i2c.mask_clk_mask = clk_mask;
 		i2c.mask_data_mask = data_mask;
 		i2c.a_clk_mask = clk_mask;
@@ -579,7 +580,19 @@ static struct radeon_i2c_bus_rec combios_setup_i2c_bus(struct radeon_device *rde
 		i2c.en_data_mask = data_mask;
 		i2c.y_clk_mask = clk_mask;
 		i2c.y_data_mask = data_mask;
+	} else if ((ddc_line == RADEON_GPIOPAD_MASK) ||
+		   (ddc_line == RADEON_MDGPIO_MASK)) {
+		/* default gpiopad masks */
+		i2c.mask_clk_mask = (0x20 << 8);
+		i2c.mask_data_mask = 0x80;
+		i2c.a_clk_mask = (0x20 << 8);
+		i2c.a_data_mask = 0x80;
+		i2c.en_clk_mask = (0x20 << 8);
+		i2c.en_data_mask = 0x80;
+		i2c.y_clk_mask = (0x20 << 8);
+		i2c.y_data_mask = 0x80;
 	} else {
+		/* default masks for ddc pads */
 		i2c.mask_clk_mask = RADEON_GPIO_EN_1;
 		i2c.mask_data_mask = RADEON_GPIO_EN_0;
 		i2c.a_clk_mask = RADEON_GPIO_A_1;