HID: Intel-thc-hid: Intel-quicki2c: Support writing output report format

There are two output formats requested in the HID-over-I2C specification:
- Command format (set feature/set report): encoded command written to
  command register, followed by data written to data register
- Output report format: all data written directly to output register

Current quicki2c_init_write_buf() implementation only supports the
command format.

Extend quicki2c_init_write_buf() to automatically detect the output
format based on the presence of command parameters and prepare the
appropriate output buffer accordingly.

Tested-by: Rui Zhang <rui1.zhang@intel.com>
Signed-off-by: Even Xu <even.xu@intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

Author: Evenxf

drivers/hid/intel-thc-hid/intel-quicki2c/quicki2c-protocol.c

@@ -30,13 +30,18 @@ static ssize_t quicki2c_init_write_buf(struct quicki2c_device *qcdev, u32 cmd, s
 	if (buf_len > write_buf_len)
 		return -EINVAL;
 
-	memcpy(write_buf, &qcdev->dev_desc.cmd_reg, HIDI2C_REG_LEN);
-	offset += HIDI2C_REG_LEN;
-	memcpy(write_buf + offset, &cmd, cmd_len);
-	offset += cmd_len;
+	if (cmd_len) {
+		memcpy(write_buf, &qcdev->dev_desc.cmd_reg, HIDI2C_REG_LEN);
+		offset += HIDI2C_REG_LEN;
+		memcpy(write_buf + offset, &cmd, cmd_len);
+		offset += cmd_len;
 
-	if (append_data_reg) {
-		memcpy(write_buf + offset, &qcdev->dev_desc.data_reg, HIDI2C_REG_LEN);
+		if (append_data_reg) {
+			memcpy(write_buf + offset, &qcdev->dev_desc.data_reg, HIDI2C_REG_LEN);
+			offset += HIDI2C_REG_LEN;
+		}
+	} else {
+		memcpy(write_buf, &qcdev->dev_desc.output_reg, HIDI2C_REG_LEN);
 		offset += HIDI2C_REG_LEN;
 	}