ALSA: usb-audio: scarlett2: Update initialisation sequence

The old initialisation code only works with Gen 2 devices. Replace it
with an initialisation sequence that works on both Gen 2 and Gen 3
devices.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/6e5c4fedb74b813872f6a4b7fba30b6c471fa63a.1624294591.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -453,10 +453,12 @@ static int scarlett2_get_port_start_num(const struct scarlett2_ports *ports,
 #define SCARLETT2_USB_NOTIFY_MONITOR  0x00400000
 
 /* Commands for sending/receiving requests/responses */
+#define SCARLETT2_USB_CMD_INIT 0
 #define SCARLETT2_USB_CMD_REQ  2
 #define SCARLETT2_USB_CMD_RESP 3
 
-#define SCARLETT2_USB_INIT_SEQ  0x00000000
+#define SCARLETT2_USB_INIT_1    0x00000000
+#define SCARLETT2_USB_INIT_2    0x00000002
 #define SCARLETT2_USB_GET_METER 0x00001001
 #define SCARLETT2_USB_GET_MIX   0x00002001
 #define SCARLETT2_USB_SET_MIX   0x00002002
@@ -650,14 +652,19 @@ static int scarlett2_usb(
 	if (err != resp_buf_size) {
 		usb_audio_err(
 			mixer->chip,
-			"Scarlett Gen 2 USB response result cmd %x was %d\n",
-			cmd, err);
+			"Scarlett Gen 2 USB response result cmd %x was %d "
+			"expected %d\n",
+			cmd, err, resp_buf_size);
 		err = -EINVAL;
 		goto unlock;
 	}
 
+	/* cmd/seq/size should match except when initialising
+	 * seq sent = 1, response = 0
+	 */
 	if (resp->cmd != req->cmd ||
-	    resp->seq != req->seq ||
+	    (resp->seq != req->seq &&
+		(le16_to_cpu(req->seq) != 1 || resp->seq != 0)) ||
 	    resp_size != le16_to_cpu(resp->size) ||
 	    resp->error ||
 	    resp->pad) {
@@ -675,7 +682,7 @@ static int scarlett2_usb(
 		goto unlock;
 	}
 
-	if (resp_size > 0)
+	if (resp_data && resp_size > 0)
 		memcpy(resp_data, resp->data, resp_size);
 
 unlock:
@@ -1924,13 +1931,12 @@ static int scarlett2_find_fc_interface(struct usb_device *dev,
 	return -EINVAL;
 }
 
-/* Initialise private data, sequence number, and get the USB data */
+/* Initialise private data */
 static int scarlett2_init_private(struct usb_mixer_interface *mixer,
 				  const struct scarlett2_device_info *info)
 {
 	struct scarlett2_data *private =
 		kzalloc(sizeof(struct scarlett2_data), GFP_KERNEL);
-	int err;
 
 	if (!private)
 		return -ENOMEM;
@@ -1948,12 +1954,35 @@ static int scarlett2_init_private(struct usb_mixer_interface *mixer,
 	private->scarlett2_seq = 0;
 	private->mixer = mixer;
 
-	err = scarlett2_find_fc_interface(mixer->chip->dev, private);
+	return scarlett2_find_fc_interface(mixer->chip->dev, private);
+}
+
+/* Cargo cult proprietary initialisation sequence */
+static int scarlett2_usb_init(struct usb_mixer_interface *mixer)
+{
+	struct usb_device *dev = mixer->chip->dev;
+	struct scarlett2_data *private = mixer->private_data;
+	u8 buf[24];
+	int err;
+
+	if (usb_pipe_type_check(dev, usb_sndctrlpipe(dev, 0)))
+		return -EINVAL;
+
+	/* step 0 */
+	err = scarlett2_usb_rx(dev, private->bInterfaceNumber,
+			       SCARLETT2_USB_CMD_INIT, buf, sizeof(buf));
 	if (err < 0)
 		return err;
 
-	/* Initialise the sequence number used for the proprietary commands */
-	return scarlett2_usb(mixer, SCARLETT2_USB_INIT_SEQ, NULL, 0, NULL, 0);
+	/* step 1 */
+	private->scarlett2_seq = 1;
+	err = scarlett2_usb(mixer, SCARLETT2_USB_INIT_1, NULL, 0, NULL, 0);
+	if (err < 0)
+		return err;
+
+	/* step 2 */
+	private->scarlett2_seq = 1;
+	return scarlett2_usb(mixer, SCARLETT2_USB_INIT_2, NULL, 0, NULL, 84);
 }
 
 /* Read configuration from the interface on start */
@@ -2128,11 +2157,16 @@ static int snd_scarlett_gen2_controls_create(struct usb_mixer_interface *mixer,
 {
 	int err;
 
-	/* Initialise private data, sequence number, and get the USB data */
+	/* Initialise private data */
 	err = scarlett2_init_private(mixer, info);
 	if (err < 0)
 		return err;
 
+	/* Send proprietary USB initialisation sequence */
+	err = scarlett2_usb_init(mixer);
+	if (err < 0)
+		return err;
+
 	/* Read volume levels and controls from the interface */
 	err = scarlett2_read_configs(mixer);
 	if (err < 0)