[PATCH 09/15] ALSA: line6: Add hwdep interface to access the POD control messages

[Andrej Krutak <dev@andree.sk>]

We must do it this way, because e.g. POD X3 won't play any sound unless
the host listens on the bulk EP, so we cannot export it only via libusb.

The driver currently doesn't use the bulk EP messages in other way,
in future it could e.g. sense/modify volume(s).

Signed-off-by: Andrej Krutak <dev@andree.sk>
---
 include/uapi/sound/asound.h |   3 +-
 sound/usb/line6/driver.c    | 167 ++++++++++++++++++++++++++++++++++++++++++++
 sound/usb/line6/driver.h    |  12 ++++
 3 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 609cadb..be353a7 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -106,9 +106,10 @@ enum {
 	SNDRV_HWDEP_IFACE_FW_OXFW,	/* Oxford OXFW970/971 based device */
 	SNDRV_HWDEP_IFACE_FW_DIGI00X,	/* Digidesign Digi 002/003 family */
 	SNDRV_HWDEP_IFACE_FW_TASCAM,	/* TASCAM FireWire series */
+	SNDRV_HWDEP_IFACE_LINE6,	/* Line6 USB processors */
 
 	/* Don't forget to change the following: */
-	SNDRV_HWDEP_IFACE_LAST = SNDRV_HWDEP_IFACE_FW_TASCAM
+	SNDRV_HWDEP_IFACE_LAST = SNDRV_HWDEP_IFACE_LINE6
 };
 
 struct snd_hwdep_info {
diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index 8a71d45..0a0e324 100644
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -14,9 +14,11 @@
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/usb.h>
+#include <linux/circ_buf.h>
 
 #include <sound/core.h>
 #include <sound/initval.h>
+#include <sound/hwdep.h>
 
 #include "capture.h"
 #include "driver.h"
@@ -315,8 +317,11 @@ static void line6_data_received(struct urb *urb)
 				line6->process_message(line6);
 		}
 	} else {
+		line6->buffer_message = urb->transfer_buffer;
+		line6->message_length = urb->actual_length;
 		if (line6->process_message)
 			line6->process_message(line6);
+		line6->buffer_message = NULL;
 	}
 
 	line6_start_listen(line6);
@@ -522,6 +527,163 @@ static void line6_get_interval(struct usb_line6 *line6)
 	}
 }
 
+
+/* Enable buffering of incoming messages, flush the buffer */
+static int line6_hwdep_open(struct snd_hwdep *hw, struct file *file)
+{
+	struct usb_line6 *line6 = hw->private_data;
+
+	/* NOTE: hwdep already provides atomicity (exclusive == true), but for
+	 * sure... */
+	if (test_and_set_bit(0, &line6->buffer_circular.active))
+		return -EBUSY;
+
+	line6->buffer_circular.head = 0;
+	line6->buffer_circular.tail = 0;
+	sema_init(&line6->buffer_circular.sem, 0);
+
+	line6->buffer_circular.active = 1;
+
+	line6->buffer_circular.data =
+		kmalloc(LINE6_MESSAGE_MAXLEN * LINE6_MESSAGE_MAXCOUNT, GFP_KERNEL);
+	if (!line6->buffer_circular.data) {
+		return -ENOMEM;
+	}
+	line6->buffer_circular.data_len =
+		kmalloc(sizeof(*line6->buffer_circular.data_len) *
+			LINE6_MESSAGE_MAXCOUNT, GFP_KERNEL);
+	if (!line6->buffer_circular.data_len) {
+		kfree(line6->buffer_circular.data);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+/* Stop buffering */
+static int line6_hwdep_release(struct snd_hwdep *hw, struct file *file)
+{
+	struct usb_line6 *line6 = hw->private_data;
+
+	/* By this time, no readers are waiting, we can safely recreate the
+	 * semaphore at next open. */
+	line6->buffer_circular.active = 0;
+
+	kfree(line6->buffer_circular.data);
+	kfree(line6->buffer_circular.data_len);
+	return 0;
+}
+
+/* Read from circular buffer, return to user */
+static long
+line6_hwdep_read(struct snd_hwdep *hwdep, char __user *buf, long count,
+					loff_t *offset)
+{
+	struct usb_line6 *line6 = hwdep->private_data;
+	unsigned long tail;
+
+	if (down_interruptible(&line6->buffer_circular.sem)) {
+		return -ERESTARTSYS;
+	}
+	/* There must an item now in the buffer... */
+
+	tail = line6->buffer_circular.tail;
+
+	if (line6->buffer_circular.data_len[tail] > count) {
+		/* Buffer too small; allow re-read of the current item... */
+		up(&line6->buffer_circular.sem);
+		return -EINVAL;
+	}
+
+	if (copy_to_user(buf,
+		&line6->buffer_circular.data[tail * LINE6_MESSAGE_MAXLEN],
+		line6->buffer_circular.data_len[tail])
+	) {
+		rv = -EFAULT;
+		goto end;
+	} else {
+		rv = line6->buffer_circular.data_len[tail];
+	}
+
+	smp_store_release(&line6->buffer_circular.tail,
+				(tail + 1) & (LINE6_MESSAGE_MAXCOUNT - 1));
+
+	return 0;
+}
+
+/* Write directly (no buffering) to device by user*/
+static long
+line6_hwdep_write(struct snd_hwdep *hwdep, const char __user *data, long count,
+					loff_t *offset)
+{
+	struct usb_line6 *line6 = hwdep->private_data;
+	int rv;
+	char *data_copy;
+
+	data_copy = kmalloc(count, GFP_ATOMIC);
+	if (!data_copy)
+		return -ENOMEM;
+
+	if (copy_from_user(data_copy, data, count))
+		rv = -EFAULT;
+	else
+		rv = line6_send_raw_message(line6, data_copy, count);
+
+	kfree(data_copy);
+	return rv;
+}
+
+static const struct snd_hwdep_ops hwdep_ops = {
+	.open    = line6_hwdep_open,
+	.release = line6_hwdep_release,
+	.read    = line6_hwdep_read,
+	.write   = line6_hwdep_write,
+};
+
+/* Insert into circular buffer */
+static void line6_hwdep_push_message(struct usb_line6 *line6)
+{
+	unsigned long head = line6->buffer_circular.head;
+	/* The spin_unlock() and next spin_lock() provide needed ordering. */
+	unsigned long tail = ACCESS_ONCE(line6->buffer_circular.tail);
+
+	if (!line6->buffer_circular.active)
+		return;
+
+	if (CIRC_SPACE(head, tail, LINE6_MESSAGE_MAXCOUNT) >= 1) {
+		unsigned char *item = &line6->buffer_circular.data[
+			head * LINE6_MESSAGE_MAXLEN];
+		memcpy(item, line6->buffer_message, line6->message_length);
+		line6->buffer_circular.data_len[head] = line6->message_length;
+
+		smp_store_release(&line6->buffer_circular.head,
+				  (head + 1) & (LINE6_MESSAGE_MAXCOUNT - 1));
+		up(&line6->buffer_circular.sem);
+	}
+}
+
+static int line6_hwdep_init(struct usb_line6 *line6)
+{
+	int err;
+	struct snd_hwdep *hwdep;
+
+	/* TODO: usb_driver_claim_interface(); */
+	line6->process_message = line6_hwdep_push_message;
+
+	line6->buffer_circular.active = 0;
+	err = snd_hwdep_new(line6->card, "config", 0, &hwdep);
+	if (err < 0)
+		goto end;
+	strcpy(hwdep->name, "config");
+	hwdep->iface = SNDRV_HWDEP_IFACE_LINE6;
+	hwdep->ops = hwdep_ops;
+	hwdep->private_data = line6;
+	hwdep->exclusive = true;
+
+end:
+	return err;
+}
+
 static int line6_init_cap_control(struct usb_line6 *line6)
 {
 	int ret;
@@ -539,6 +701,10 @@ static int line6_init_cap_control(struct usb_line6 *line6)
 		line6->buffer_message = kmalloc(LINE6_MESSAGE_MAXLEN, GFP_KERNEL);
 		if (!line6->buffer_message)
 			return -ENOMEM;
+	} else {
+		ret = line6_hwdep_init(line6);
+		if (ret < 0)
+			return ret;
 	}
 
 	ret = line6_start_listen(line6);
@@ -716,3 +882,4 @@ EXPORT_SYMBOL_GPL(line6_resume);
 MODULE_AUTHOR(DRIVER_AUTHOR);
 MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("GPL");
+
diff --git a/sound/usb/line6/driver.h b/sound/usb/line6/driver.h
index 71ad299..f4ab6cd 100644
--- a/sound/usb/line6/driver.h
+++ b/sound/usb/line6/driver.h
@@ -33,6 +33,8 @@
 #define LINE6_TIMEOUT (1)
 #define LINE6_BUFSIZE_LISTEN (64)
 #define LINE6_MESSAGE_MAXLEN (256)
+/* Must be 2^n; 4k packets are common, MAXLEN * MAXCOUNT should be bigger... */
+#define LINE6_MESSAGE_MAXCOUNT (1 << 5)
 
 /*
 	Line 6 MIDI control commands
@@ -155,6 +157,16 @@ struct usb_line6 {
 	/* Length of message to be processed, generated from MIDI layer  */
 	int message_length;
 
+	/* Circular buffer for non-MIDI control messages */
+	struct {
+		int active;
+		char *data;
+		int *data_len;
+		unsigned long head, tail;
+		/* Actually is up'd # of items in the buffer - times */
+		struct semaphore sem;
+	} buffer_circular;
+
 	/* If MIDI is supported, buffer_message contains the pre-processed data;
 	 * otherwise the data is only in urb_listen (buffer_incoming). */
 	void (*process_message)(struct usb_line6 *);
-- 
1.9.1