1 files changed, 53 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index de5144c8c15..f899afd924b 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -462,14 +462,63 @@ static int intel_sdvo_get_pixel_multiplier(struct drm_display_mode *mode)
 }
 
 /**
- * Don't check status code from this as it switches the bus back to the
- * SDVO chips which defeats the purpose of doing a bus switch in the first
- * place.
+ * Try to read the response after issuie the DDC switch command. But it
+ * is noted that we must do the action of reading response and issuing DDC
+ * switch command in one I2C transaction. Otherwise when we try to start
+ * another I2C transaction after issuing the DDC bus switch, it will be
+ * switched to the internal SDVO register.
  */
 static void intel_sdvo_set_control_bus_switch(struct intel_output *intel_output,
 					      u8 target)
 {
-	intel_sdvo_write_cmd(intel_output, SDVO_CMD_SET_CONTROL_BUS_SWITCH, &target, 1);
+	struct intel_sdvo_priv *sdvo_priv = intel_output->dev_priv;
+	u8 out_buf[2], cmd_buf[2], ret_value[2], ret;
+	struct i2c_msg msgs[] = {
+		{
+			.addr = sdvo_priv->slave_addr >> 1,
+			.flags = 0,
+			.len = 2,
+			.buf = out_buf,
+		},
+		/* the following two are to read the response */
+		{
+			.addr = sdvo_priv->slave_addr >> 1,
+			.flags = 0,
+			.len = 1,
+			.buf = cmd_buf,
+		},
+		{
+			.addr = sdvo_priv->slave_addr >> 1,
+			.flags = I2C_M_RD,
+			.len = 1,
+			.buf = ret_value,
+		},
+	};
+
+	intel_sdvo_debug_write(intel_output, SDVO_CMD_SET_CONTROL_BUS_SWITCH,
+					&target, 1);
+	/* write the DDC switch command argument */
+	intel_sdvo_write_byte(intel_output, SDVO_I2C_ARG_0, target);
+
+	out_buf[0] = SDVO_I2C_OPCODE;
+	out_buf[1] = SDVO_CMD_SET_CONTROL_BUS_SWITCH;
+	cmd_buf[0] = SDVO_I2C_CMD_STATUS;
+	cmd_buf[1] = 0;
+	ret_value[0] = 0;
+	ret_value[1] = 0;
+
+	ret = i2c_transfer(intel_output->i2c_bus, msgs, 3);
+	if (ret != 3) {
+		/* failure in I2C transfer */
+		DRM_DEBUG_KMS("I2c transfer returned %d\n", ret);
+		return;
+	}
+	if (ret_value[0] != SDVO_CMD_STATUS_SUCCESS) {
+		DRM_DEBUG_KMS("DDC switch command returns response %d\n",
+					ret_value[0]);
+		return;
+	}
+	return;
 }
 
 static bool intel_sdvo_set_target_input(struct intel_output *intel_output, bool target_0, bool target_1)