drm/radeon/kms/DCE3+: switch pads to ddc mode when going i2c

The pins for ddc and aux are shared so you need to switch the
mode when doing ddc.  The ProcessAuxChannel table already sets
the pin mode to DP.  This should fix unreliable ddc issues
on DP ports using non-DP monitors.
Signed-off-by: NAlex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_i2c.c

@@ -99,6 +99,13 @@ static void radeon_i2c_do_lock(struct radeon_i2c_chan *i2c, int lock_state)
 		}
 	}
 
+	/* switch the pads to ddc mode */
+	if (ASIC_IS_DCE3(rdev) && rec->hw_capable) {
+		temp = RREG32(rec->mask_clk_reg);
+		temp &= ~(1 << 16);
+		WREG32(rec->mask_clk_reg, temp);
+	}
+
 	/* clear the output pin values */
 	temp = RREG32(rec->a_clk_reg) & ~rec->a_clk_mask;
 	WREG32(rec->a_clk_reg, temp);