[PATCH] ALSA: usb-audio: Add quirk for MOTU MicroBook II

[PATCH] ALSA: usb-audio: Add quirk for MOTU MicroBook II

[Manuel Reinhardt]

Add an entry to the quirks-table to for usb-audio to recognize the
Microbook II (although it only exposes vendor interfaces). A simple boot
quirk is also implemented to set up the sample rate and  make sure that
no audio urbs are sent before the device is ready.

This patch only provides audio playback and capture at 96kHz sample
rate. Notice the following shortcomings:

- The sample rate is currently hardcoded to 96k although the device also
  supports 48k and 44.1k.

- The various mixer controls of the MicroBook are not made available.

- The keep-iface control should be on by default because the device
  shuts down whenever the altsetting is reset which is usually unwanted.
  (I don't know the best way to do this)

- The communication format used by the MicroBook for sample rate setting
  and also other setup has been reverse engineered by looking at the
  usbmon output while running the windows driver through virtualbox. In
  this patch the first byte of every message is set to \0 while in the
  observed communications the first byte acts as a "message-counter"
  increasing its value with every message sent. Leaving it at \0 does
  not seem to affect the device.

Signed-off-by: Manuel Reinhardt <manuel.rhdt@gmail.com>
---
 sound/usb/pcm.c          |  4 ++
 sound/usb/quirks-table.h | 65 +++++++++++++++++++++++++++
 sound/usb/quirks.c       | 97 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 166 insertions(+)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index db114f3977e0..056af0a57b22 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -354,6 +354,10 @@ static int set_sync_ep_implicit_fb_quirk(struct snd_usb_substream *subs,
 		ep = 0x81;
 		ifnum = 1;
 		goto add_sync_ep_from_ifnum;
+	case USB_ID(0x07fd, 0x0004): /* MOTU MicroBook II */
+		ep = 0x84;
+		ifnum = 0;
+		goto add_sync_ep_from_ifnum;
 	}
 
 	if (attr == USB_ENDPOINT_SYNC_ASYNC &&
diff --git a/sound/usb/quirks-table.h b/sound/usb/quirks-table.h
index b345beb447bd..86e80916a029 100644
--- a/sound/usb/quirks-table.h
+++ b/sound/usb/quirks-table.h
@@ -3398,5 +3398,70 @@ AU0828_DEVICE(0x2040, 0x7270, "Hauppauge", "HVR-950Q"),
 		.ifnum = QUIRK_NO_INTERFACE
 	}
 },
+/* MOTU Microbook II */
+{
+	USB_DEVICE(0x07fd, 0x0004),
+	.driver_info = (unsigned long) &(const struct snd_usb_audio_quirk) {
+		.vendor_name = "MOTU",
+		.product_name = "MicroBookII",
+		.ifnum = QUIRK_ANY_INTERFACE,
+		.type = QUIRK_COMPOSITE,
+		.data = (const struct snd_usb_audio_quirk[]) {
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_STANDARD_MIXER,
+			},
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_FIXED_ENDPOINT,
+				.data = &(const struct audioformat) {
+					.formats = SNDRV_PCM_FMTBIT_S24_3BE,
+					.channels = 6,
+					.iface = 0,
+					.altsetting = 1,
+					.altset_idx = 1,
+					.attributes = 0,
+					.endpoint = 0x84,
+					.rates = SNDRV_PCM_RATE_96000,
+					.ep_attr = USB_ENDPOINT_XFER_ISOC |
+						   USB_ENDPOINT_SYNC_ASYNC,
+					.rate_min = 96000,
+					.rate_max = 96000,
+					.nr_rates = 1,
+					.maxpacksize = 0x00d8,
+					.rate_table = (unsigned int[]) {
+						96000
+					}
+				}
+			},
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_FIXED_ENDPOINT,
+				.data = &(const struct audioformat) {
+					.formats = SNDRV_PCM_FMTBIT_S24_3BE,
+					.channels = 8,
+					.iface = 0,
+					.altsetting = 1,
+					.altset_idx = 1,
+					.attributes = 0,
+					.endpoint = 0x03,
+					.rates = SNDRV_PCM_RATE_96000,
+					.ep_attr = USB_ENDPOINT_XFER_ISOC |
+						   USB_ENDPOINT_SYNC_ASYNC,
+					.rate_min = 96000,
+					.rate_max = 96000,
+					.nr_rates = 1,
+					.maxpacksize = 0x0120,
+					.rate_table = (unsigned int[]) {
+						96000
+					}
+				}
+			},
+			{
+				.ifnum = -1
+			}
+		}
+	}
+},
 
 #undef USB_DEVICE_VENDOR_SPEC
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index f372c624bbf4..c86a06dd97dd 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -1000,6 +1000,101 @@ static int snd_usb_axefx3_boot_quirk(struct usb_device *dev)
 	return 0;
 }
 
+
+#define MICROBOOK_BUF_SIZE 128
+
+static int snd_usb_motu_microbookii_communicate(struct usb_device *dev, u8 *buf,
+						int buf_size, int *length)
+{
+	int err, actual_length;
+
+	err = usb_interrupt_msg(dev, usb_sndintpipe(dev, 0x01), buf, *length,
+				&actual_length, 1000);
+	if (err < 0)
+		return err;
+
+	print_hex_dump(KERN_DEBUG, "snd: ", DUMP_PREFIX_NONE, 16, 1, buf,
+		       actual_length, false);
+
+	memset(buf, 0, buf_size);
+
+	err = usb_interrupt_msg(dev, usb_rcvintpipe(dev, 0x82), buf,
+				buf_size, &actual_length, 1000);
+	if (err < 0)
+		return err;
+
+	print_hex_dump(KERN_DEBUG, "rcv: ", DUMP_PREFIX_NONE, 16, 1, buf,
+		       actual_length, false);
+
+	*length = actual_length;
+	return 0;
+}
+
+static int snd_usb_motu_microbookii_boot_quirk(struct usb_device *dev)
+{
+	int err, actual_length, poll_attempts = 0;
+	bool setup_finished = false;
+	static const u8 set_samplerate_seq[] = { 0x00, 0x00, 0x00, 0x00,
+						 0x00, 0x00, 0x0b, 0x14,
+						 0x00, 0x00, 0x00, 0x01 };
+	static const u8 poll_ready_seq[] = { 0x00, 0x04, 0x00, 0x00,
+					     0x00, 0x00, 0x0b, 0x18 };
+	u8 *buf = kzalloc(MICROBOOK_BUF_SIZE, GFP_KERNEL);
+
+	if (!buf)
+		return -ENOMEM;
+
+	dev_info(&dev->dev, "Waiting for MOTU Microbook II to boot up...\n");
+
+	/* First we tell the device which sample rate to use. */
+	memcpy(buf, set_samplerate_seq, ARRAY_SIZE(set_samplerate_seq));
+	actual_length = ARRAY_SIZE(set_samplerate_seq);
+	err = snd_usb_motu_microbookii_communicate(dev, buf, MICROBOOK_BUF_SIZE,
+						   &actual_length);
+
+	if (err < 0) {
+		kfree(buf);
+		dev_err(&dev->dev,
+			"failed setting the sample rate for Motu MicroBook II: %d\n",
+			err);
+		return err;
+	}
+
+	/* Then we poll every 100 ms until the device informs of its readiness. */
+	while (!setup_finished) {
+		if (++poll_attempts > 100) {
+			kfree(buf);
+			dev_err(&dev->dev,
+				"failed booting Motu MicroBook II: timeout\n");
+			return -ENODEV;
+		}
+
+		memset(buf, 0, MICROBOOK_BUF_SIZE);
+		memcpy(buf, poll_ready_seq, ARRAY_SIZE(poll_ready_seq));
+
+		actual_length = ARRAY_SIZE(poll_ready_seq);
+		err = snd_usb_motu_microbookii_communicate(
+			dev, buf, MICROBOOK_BUF_SIZE, &actual_length);
+		if (err < 0) {
+			kfree(buf);
+			dev_err(&dev->dev,
+				"failed booting Motu MicroBook II: communication error\n");
+			return err;
+		}
+
+		if (buf[actual_length - 1] == 1)
+			setup_finished = true;
+
+		msleep(100);
+	}
+
+	kfree(buf);
+
+	dev_info(&dev->dev, "MOTU MicroBook II ready\n");
+
+	return 0;
+}
+
 /*
  * Setup quirks
  */
@@ -1177,6 +1272,8 @@ int snd_usb_apply_boot_quirk(struct usb_device *dev,
 		return snd_usb_gamecon780_boot_quirk(dev);
 	case USB_ID(0x2466, 0x8010): /* Fractal Audio Axe-Fx 3 */
 		return snd_usb_axefx3_boot_quirk(dev);
+	case USB_ID(0x07fd, 0x0004): /* MOTU MicroBook II */
+		return snd_usb_motu_microbookii_boot_quirk(dev);
 	}
 
 	return 0;
-- 
2.20.1

Re: [PATCH] ALSA: usb-audio: Add quirk for MOTU MicroBook II

[Takashi Iwai]

On Wed, 27 Feb 2019 15:26:01 +0100,
Manuel Reinhardt wrote:
> 
> Add an entry to the quirks-table to for usb-audio to recognize the
> Microbook II (although it only exposes vendor interfaces). A simple boot
> quirk is also implemented to set up the sample rate and  make sure that
> no audio urbs are sent before the device is ready.
> 
> This patch only provides audio playback and capture at 96kHz sample
> rate. Notice the following shortcomings:
> 
> - The sample rate is currently hardcoded to 96k although the device also
>   supports 48k and 44.1k.
> 
> - The various mixer controls of the MicroBook are not made available.
> 
> - The keep-iface control should be on by default because the device
>   shuts down whenever the altsetting is reset which is usually unwanted.
>   (I don't know the best way to do this)

Can be set either in the quirk callback you write.
Or it'd be not bad to create a white list, too.

> +static int snd_usb_motu_microbookii_boot_quirk(struct usb_device *dev)
> +{
> +	int err, actual_length, poll_attempts = 0;
> +	bool setup_finished = false;
> +	static const u8 set_samplerate_seq[] = { 0x00, 0x00, 0x00, 0x00,
> +						 0x00, 0x00, 0x0b, 0x14,
> +						 0x00, 0x00, 0x00, 0x01 };
> +	static const u8 poll_ready_seq[] = { 0x00, 0x04, 0x00, 0x00,
> +					     0x00, 0x00, 0x0b, 0x18 };
> +	u8 *buf = kzalloc(MICROBOOK_BUF_SIZE, GFP_KERNEL);
> +
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	dev_info(&dev->dev, "Waiting for MOTU Microbook II to boot up...\n");
> +
> +	/* First we tell the device which sample rate to use. */
> +	memcpy(buf, set_samplerate_seq, ARRAY_SIZE(set_samplerate_seq));

This is about byte-size, so better to use sizeof().
ARRAY_SIZE() confuses readers as if he needs to care about the
type.

> +	actual_length = ARRAY_SIZE(set_samplerate_seq);

Ditto here.  Also some other codes below, too.

> +	err = snd_usb_motu_microbookii_communicate(dev, buf, MICROBOOK_BUF_SIZE,
> +						   &actual_length);
> +
> +	if (err < 0) {
> +		kfree(buf);
> +		dev_err(&dev->dev,
> +			"failed setting the sample rate for Motu MicroBook II: %d\n",
> +			err);
> +		return err;

Since kfree() is mandatory in the error path, it's better to use goto
and kfree() there, instead of spreading over all places.

> +	}
> +
> +	/* Then we poll every 100 ms until the device informs of its readiness. */
> +	while (!setup_finished) {
> +		if (++poll_attempts > 100) {
> +			kfree(buf);
> +			dev_err(&dev->dev,
> +				"failed booting Motu MicroBook II: timeout\n");
> +			return -ENODEV;
> +		}
> +
> +		memset(buf, 0, MICROBOOK_BUF_SIZE);
> +		memcpy(buf, poll_ready_seq, ARRAY_SIZE(poll_ready_seq));
> +
> +		actual_length = ARRAY_SIZE(poll_ready_seq);
> +		err = snd_usb_motu_microbookii_communicate(
> +			dev, buf, MICROBOOK_BUF_SIZE, &actual_length);
> +		if (err < 0) {
> +			kfree(buf);
> +			dev_err(&dev->dev,
> +				"failed booting Motu MicroBook II: communication error\n");
> +			return err;
> +		}
> +
> +		if (buf[actual_length - 1] == 1)
> +			setup_finished = true;

I wouldn't trust the returned value.  Let's be paranoid and check
whether the actual_length is within the expected range.

> +
> +		msleep(100);

BTW, setup_finished is superfluous.  You can just write like

		msleep(100);
		if (buf[actual_lenght - 1] == 1)
			break;

Or if 100ms sleep isn't needed in the successful case, it can be

		if (buf[actual_lenght - 1] == 1)
			break;
		msleep(100);
		

thanks,

Takashi

[PATCH] ALSA: usb-audio: Add quirk for MOTU MicroBook II

[Manuel Reinhardt]

Add an entry to the quirks-table to for usb-audio to recognize the
Microbook II (although it only exposes vendor interfaces). A simple boot
quirk is also implemented to set up the sample rate and  make sure that
no audio urbs are sent before the device is ready.

This patch only provides audio playback and capture at 96kHz sample
rate. Notice the following shortcomings:

- The sample rate is currently hardcoded to 96k although the device also
  supports 48k and 44.1k.

- The various mixer controls of the MicroBook are not made available.

- The keep-iface control should be on by default because the device
  shuts down whenever the altsetting is reset which is usually unwanted.
  (I don't know the best way to do this)

- The communication format used by the MicroBook for sample rate setting
  and also other setup has been reverse engineered by looking at the
  usbmon output while running the windows driver through virtualbox. In
  this patch the first byte of every message is set to \0 while in the
  observed communications the first byte acts as a "message-counter"
  increasing its value with every message sent. Leaving it at \0 does
  not seem to affect the device.

Signed-off-by: Manuel Reinhardt <manuel.rhdt@gmail.com>
---
 sound/usb/pcm.c          |   4 ++
 sound/usb/quirks-table.h |  65 +++++++++++++++++++++++++
 sound/usb/quirks.c       | 101 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 170 insertions(+)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index db114f3977e0..056af0a57b22 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -354,6 +354,10 @@ static int set_sync_ep_implicit_fb_quirk(struct snd_usb_substream *subs,
 		ep = 0x81;
 		ifnum = 1;
 		goto add_sync_ep_from_ifnum;
+	case USB_ID(0x07fd, 0x0004): /* MOTU MicroBook II */
+		ep = 0x84;
+		ifnum = 0;
+		goto add_sync_ep_from_ifnum;
 	}
 
 	if (attr == USB_ENDPOINT_SYNC_ASYNC &&
diff --git a/sound/usb/quirks-table.h b/sound/usb/quirks-table.h
index b345beb447bd..86e80916a029 100644
--- a/sound/usb/quirks-table.h
+++ b/sound/usb/quirks-table.h
@@ -3398,5 +3398,70 @@ AU0828_DEVICE(0x2040, 0x7270, "Hauppauge", "HVR-950Q"),
 		.ifnum = QUIRK_NO_INTERFACE
 	}
 },
+/* MOTU Microbook II */
+{
+	USB_DEVICE(0x07fd, 0x0004),
+	.driver_info = (unsigned long) &(const struct snd_usb_audio_quirk) {
+		.vendor_name = "MOTU",
+		.product_name = "MicroBookII",
+		.ifnum = QUIRK_ANY_INTERFACE,
+		.type = QUIRK_COMPOSITE,
+		.data = (const struct snd_usb_audio_quirk[]) {
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_STANDARD_MIXER,
+			},
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_FIXED_ENDPOINT,
+				.data = &(const struct audioformat) {
+					.formats = SNDRV_PCM_FMTBIT_S24_3BE,
+					.channels = 6,
+					.iface = 0,
+					.altsetting = 1,
+					.altset_idx = 1,
+					.attributes = 0,
+					.endpoint = 0x84,
+					.rates = SNDRV_PCM_RATE_96000,
+					.ep_attr = USB_ENDPOINT_XFER_ISOC |
+						   USB_ENDPOINT_SYNC_ASYNC,
+					.rate_min = 96000,
+					.rate_max = 96000,
+					.nr_rates = 1,
+					.maxpacksize = 0x00d8,
+					.rate_table = (unsigned int[]) {
+						96000
+					}
+				}
+			},
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_FIXED_ENDPOINT,
+				.data = &(const struct audioformat) {
+					.formats = SNDRV_PCM_FMTBIT_S24_3BE,
+					.channels = 8,
+					.iface = 0,
+					.altsetting = 1,
+					.altset_idx = 1,
+					.attributes = 0,
+					.endpoint = 0x03,
+					.rates = SNDRV_PCM_RATE_96000,
+					.ep_attr = USB_ENDPOINT_XFER_ISOC |
+						   USB_ENDPOINT_SYNC_ASYNC,
+					.rate_min = 96000,
+					.rate_max = 96000,
+					.nr_rates = 1,
+					.maxpacksize = 0x0120,
+					.rate_table = (unsigned int[]) {
+						96000
+					}
+				}
+			},
+			{
+				.ifnum = -1
+			}
+		}
+	}
+},
 
 #undef USB_DEVICE_VENDOR_SPEC
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index f372c624bbf4..e6ce1bbe6ca6 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -1000,6 +1000,105 @@ static int snd_usb_axefx3_boot_quirk(struct usb_device *dev)
 	return 0;
 }
 
+
+#define MICROBOOK_BUF_SIZE 128
+
+static int snd_usb_motu_microbookii_communicate(struct usb_device *dev, u8 *buf,
+						int buf_size, int *length)
+{
+	int err, actual_length;
+
+	err = usb_interrupt_msg(dev, usb_sndintpipe(dev, 0x01), buf, *length,
+				&actual_length, 1000);
+	if (err < 0)
+		return err;
+
+	print_hex_dump(KERN_DEBUG, "MicroBookII snd: ", DUMP_PREFIX_NONE, 16, 1,
+		       buf, actual_length, false);
+
+	memset(buf, 0, buf_size);
+
+	err = usb_interrupt_msg(dev, usb_rcvintpipe(dev, 0x82), buf, buf_size,
+				&actual_length, 1000);
+	if (err < 0)
+		return err;
+
+	print_hex_dump(KERN_DEBUG, "MicroBookII rcv: ", DUMP_PREFIX_NONE, 16, 1,
+		       buf, actual_length, false);
+
+	*length = actual_length;
+	return 0;
+}
+
+static int snd_usb_motu_microbookii_boot_quirk(struct usb_device *dev)
+{
+	int err, actual_length, poll_attempts = 0;
+	static const u8 set_samplerate_seq[] = { 0x00, 0x00, 0x00, 0x00,
+						 0x00, 0x00, 0x0b, 0x14,
+						 0x00, 0x00, 0x00, 0x01 };
+	static const u8 poll_ready_seq[] = { 0x00, 0x04, 0x00, 0x00,
+					     0x00, 0x00, 0x0b, 0x18 };
+	u8 *buf = kzalloc(MICROBOOK_BUF_SIZE, GFP_KERNEL);
+
+	if (!buf)
+		return -ENOMEM;
+
+	dev_info(&dev->dev, "Waiting for MOTU Microbook II to boot up...\n");
+
+	/* First we tell the device which sample rate to use. */
+	memcpy(buf, set_samplerate_seq, sizeof(set_samplerate_seq));
+	actual_length = sizeof(set_samplerate_seq);
+	err = snd_usb_motu_microbookii_communicate(dev, buf, MICROBOOK_BUF_SIZE,
+						   &actual_length);
+
+	if (err < 0) {
+		dev_err(&dev->dev,
+			"failed setting the sample rate for Motu MicroBook II: %d\n",
+			err);
+		goto free_buf;
+	}
+
+	/* Then we poll every 100 ms until the device informs of its readiness. */
+	while (true) {
+		if (++poll_attempts > 100) {
+			dev_err(&dev->dev,
+				"failed booting Motu MicroBook II: timeout\n");
+			err = -ENODEV;
+			goto free_buf;
+		}
+
+		memset(buf, 0, MICROBOOK_BUF_SIZE);
+		memcpy(buf, poll_ready_seq, sizeof(poll_ready_seq));
+
+		actual_length = sizeof(poll_ready_seq);
+		err = snd_usb_motu_microbookii_communicate(
+			dev, buf, MICROBOOK_BUF_SIZE, &actual_length);
+		if (err < 0) {
+			dev_err(&dev->dev,
+				"failed booting Motu MicroBook II: communication error %d\n",
+				err);
+			goto free_buf;
+		}
+
+		/* the device signals its readiness through a message of the
+		 * form
+		 *           XX 06 00 00 00 00 0b 18  00 00 00 01
+		 * If the device is not yet ready to accept audio data, the
+		 * last byte of that sequence is 00.
+		 */
+		if (actual_length == 12 && buf[actual_length - 1] == 1)
+			break;
+
+		msleep(100);
+	}
+
+	dev_info(&dev->dev, "MOTU MicroBook II ready\n");
+
+free_buf:
+	kfree(buf);
+	return err;
+}
+
 /*
  * Setup quirks
  */
@@ -1177,6 +1276,8 @@ int snd_usb_apply_boot_quirk(struct usb_device *dev,
 		return snd_usb_gamecon780_boot_quirk(dev);
 	case USB_ID(0x2466, 0x8010): /* Fractal Audio Axe-Fx 3 */
 		return snd_usb_axefx3_boot_quirk(dev);
+	case USB_ID(0x07fd, 0x0004): /* MOTU MicroBook II */
+		return snd_usb_motu_microbookii_boot_quirk(dev);
 	}
 
 	return 0;
-- 
2.20.1

Re: [PATCH] ALSA: usb-audio: Add quirk for MOTU MicroBook II

[Manuel Reinhardt]

Thank you for your time and comments.

Am Mittwoch, den 27.02.2019, 18:14 +0100 schrieb Takashi Iwai:
> On Wed, 27 Feb 2019 15:26:01 +0100,
> Manuel Reinhardt wrote:
> > Add an entry to the quirks-table to for usb-audio to recognize the
> > Microbook II (although it only exposes vendor interfaces). A simple
> > boot
> > quirk is also implemented to set up the sample rate and  make sure
> > that
> > no audio urbs are sent before the device is ready.
> > 
> > This patch only provides audio playback and capture at 96kHz sample
> > rate. Notice the following shortcomings:
> > 
> > - The sample rate is currently hardcoded to 96k although the device
> > also
> >   supports 48k and 44.1k.
> > 
> > - The various mixer controls of the MicroBook are not made
> > available.
> > 
> > - The keep-iface control should be on by default because the device
> >   shuts down whenever the altsetting is reset which is usually
> > unwanted.
> >   (I don't know the best way to do this)
> 
> Can be set either in the quirk callback you write.
> Or it'd be not bad to create a white list, too.

I will try to address that in a future patch.

I have fixed the patch to address your remaining concerns.

Re: [PATCH] ALSA: usb-audio: Add quirk for MOTU MicroBook II

[Takashi Iwai]

On Thu, 28 Feb 2019 20:34:04 +0100,
Manuel Reinhardt wrote:
> 
> Add an entry to the quirks-table to for usb-audio to recognize the
> Microbook II (although it only exposes vendor interfaces). A simple boot
> quirk is also implemented to set up the sample rate and  make sure that
> no audio urbs are sent before the device is ready.
> 
> This patch only provides audio playback and capture at 96kHz sample
> rate. Notice the following shortcomings:
> 
> - The sample rate is currently hardcoded to 96k although the device also
>   supports 48k and 44.1k.
> 
> - The various mixer controls of the MicroBook are not made available.
> 
> - The keep-iface control should be on by default because the device
>   shuts down whenever the altsetting is reset which is usually unwanted.
>   (I don't know the best way to do this)
> 
> - The communication format used by the MicroBook for sample rate setting
>   and also other setup has been reverse engineered by looking at the
>   usbmon output while running the windows driver through virtualbox. In
>   this patch the first byte of every message is set to \0 while in the
>   observed communications the first byte acts as a "message-counter"
>   increasing its value with every message sent. Leaving it at \0 does
>   not seem to affect the device.
> 
> Signed-off-by: Manuel Reinhardt <manuel.rhdt@gmail.com>

Applied, thanks.


Takashi