HID: i2c-hid: support sending HID output reports using the output register

The current i2c hid driver does not support sending HID output reports using
the output register for devices which support receiving reports through this
method. This patch determines which method to use to send output reports based
 on the value of wMaxOutputLength in the device's HID descriptor.
Signed-off-by: Andrew Duggan <aduggan@synaptics.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/i2c-hid/i2c-hid.c

@@ -108,6 +108,7 @@ static const struct i2c_hid_cmd hid_reset_cmd =		{ I2C_HID_CMD(0x01),
 static const struct i2c_hid_cmd hid_get_report_cmd =	{ I2C_HID_CMD(0x02) };
 static const struct i2c_hid_cmd hid_set_report_cmd =	{ I2C_HID_CMD(0x03) };
 static const struct i2c_hid_cmd hid_set_power_cmd =	{ I2C_HID_CMD(0x08) };
+static const struct i2c_hid_cmd hid_no_cmd =		{ .length = 0 };
 
 /*
  * These definitions are not used here, but are defined by the spec.
@@ -259,8 +260,11 @@ static int i2c_hid_set_report(struct i2c_client *client, u8 reportType,
 {
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
 	u8 *args = ihid->argsbuf;
+	const struct i2c_hid_cmd * hidcmd = &hid_set_report_cmd;
 	int ret;
 	u16 dataRegister = le16_to_cpu(ihid->hdesc.wDataRegister);
+	u16 outputRegister = le16_to_cpu(ihid->hdesc.wOutputRegister);
+	u16 maxOutputLength = le16_to_cpu(ihid->hdesc.wMaxOutputLength);
 
 	/* hidraw already checked that data_len < HID_MAX_BUFFER_SIZE */
 	u16 size =	2			/* size */ +
@@ -278,8 +282,18 @@ static int i2c_hid_set_report(struct i2c_client *client, u8 reportType,
 		reportID = 0x0F;
 	}
 
+	/*
+	 * use the data register for feature reports or if the device does not
+	 * support the output register
+	 */
+	if (reportType == 0x03 || maxOutputLength == 0) {
 		args[index++] = dataRegister & 0xFF;
 		args[index++] = dataRegister >> 8;
+	} else {
+		args[index++] = outputRegister & 0xFF;
+		args[index++] = outputRegister >> 8;
+		hidcmd = &hid_no_cmd;
+	}
 
 	args[index++] = size & 0xFF;
 	args[index++] = size >> 8;
@@ -289,7 +303,7 @@ static int i2c_hid_set_report(struct i2c_client *client, u8 reportType,
 
 	memcpy(&args[index], buf, data_len);
 
-	ret = __i2c_hid_command(client, &hid_set_report_cmd, reportID,
+	ret = __i2c_hid_command(client, hidcmd, reportID,
 		reportType, args, args_len, NULL, 0);
 	if (ret) {
 		dev_err(&client->dev, "failed to set a report to device.\n");