[PATCH 1/3] usb: gadget: f_uac2/u_audio: add feedback endpoint support

[Ruslan Bilovol <ruslan.bilovol@gmail.com>]

As per USB and UAC2 specs, asynchronous audio sink endpoint
requires explicit synchronization mechanism (Isochronous
Feedback Endpoint)

Implement feedback companion endpoint for ISO OUT endpoint

This patch adds all required infrastructure and USB requests
handling for feedback endpoint. Syncrhonization itself is
still dummy (feedback ep always reports 'nomimal frequency'
 e.g. no adjustement is needed). This satisfies hosts that
require feedback endpoint (like Win10) and poll it periodically

Actual synchronization mechanism should be implemented
separately

Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
---
 drivers/usb/gadget/function/f_uac2.c  |  34 +++++++++-
 drivers/usb/gadget/function/u_audio.c | 124 +++++++++++++++++++++++++++++++++-
 drivers/usb/gadget/function/u_audio.h |   3 +
 3 files changed, 158 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index fb9b875..a57bf77 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -237,7 +237,7 @@ enum {
 	.bDescriptorType = USB_DT_INTERFACE,
 
 	.bAlternateSetting = 1,
-	.bNumEndpoints = 1,
+	.bNumEndpoints = 2,
 	.bInterfaceClass = USB_CLASS_AUDIO,
 	.bInterfaceSubClass = USB_SUBCLASS_AUDIOSTREAMING,
 	.bInterfaceProtocol = UAC_VERSION_2,
@@ -296,6 +296,27 @@ enum {
 	.wLockDelay = 0,
 };
 
+/* STD AS ISO IN Feedback Endpoint */
+static struct usb_endpoint_descriptor fs_epin_fback_desc = {
+	.bLength = USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType = USB_DT_ENDPOINT,
+
+	.bEndpointAddress = USB_DIR_IN,
+	.bmAttributes = USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_USAGE_FEEDBACK,
+	.wMaxPacketSize = cpu_to_le16(3),
+	.bInterval = 1,
+};
+
+static struct usb_endpoint_descriptor hs_epin_fback_desc = {
+	.bLength = USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType = USB_DT_ENDPOINT,
+
+	.bmAttributes = USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_USAGE_FEEDBACK,
+	.wMaxPacketSize = cpu_to_le16(4),
+	.bInterval = 4,
+};
+
+
 /* Audio Streaming IN Interface - Alt0 */
 static struct usb_interface_descriptor std_as_in_if0_desc = {
 	.bLength = sizeof std_as_in_if0_desc,
@@ -392,6 +413,7 @@ enum {
 	(struct usb_descriptor_header *)&as_out_fmt1_desc,
 	(struct usb_descriptor_header *)&fs_epout_desc,
 	(struct usb_descriptor_header *)&as_iso_out_desc,
+	(struct usb_descriptor_header *)&fs_epin_fback_desc,
 
 	(struct usb_descriptor_header *)&std_as_in_if0_desc,
 	(struct usb_descriptor_header *)&std_as_in_if1_desc,
@@ -422,6 +444,7 @@ enum {
 	(struct usb_descriptor_header *)&as_out_fmt1_desc,
 	(struct usb_descriptor_header *)&hs_epout_desc,
 	(struct usb_descriptor_header *)&as_iso_out_desc,
+	(struct usb_descriptor_header *)&hs_epin_fback_desc,
 
 	(struct usb_descriptor_header *)&std_as_in_if0_desc,
 	(struct usb_descriptor_header *)&std_as_in_if1_desc,
@@ -541,6 +564,7 @@ static void setup_descriptor(struct f_uac2_opts *opts)
 		fs_audio_desc[i++] = USBDHDR(&as_out_fmt1_desc);
 		fs_audio_desc[i++] = USBDHDR(&fs_epout_desc);
 		fs_audio_desc[i++] = USBDHDR(&as_iso_out_desc);
+		fs_audio_desc[i++] = USBDHDR(&fs_epin_fback_desc);
 	}
 	if (EPIN_EN(opts)) {
 		fs_audio_desc[i++] = USBDHDR(&std_as_in_if0_desc);
@@ -574,6 +598,7 @@ static void setup_descriptor(struct f_uac2_opts *opts)
 		hs_audio_desc[i++] = USBDHDR(&as_out_fmt1_desc);
 		hs_audio_desc[i++] = USBDHDR(&hs_epout_desc);
 		hs_audio_desc[i++] = USBDHDR(&as_iso_out_desc);
+		hs_audio_desc[i++] = USBDHDR(&hs_epin_fback_desc);
 	}
 	if (EPIN_EN(opts)) {
 		hs_audio_desc[i++] = USBDHDR(&std_as_in_if0_desc);
@@ -681,6 +706,12 @@ static void setup_descriptor(struct f_uac2_opts *opts)
 			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
 			return -ENODEV;
 		}
+		agdev->in_ep_fback = usb_ep_autoconfig(gadget,
+						       &fs_epin_fback_desc);
+		if (!agdev->in_ep_fback) {
+			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
+			return -ENODEV;
+		}
 	}
 
 	if (EPIN_EN(uac2_opts)) {
@@ -699,6 +730,7 @@ static void setup_descriptor(struct f_uac2_opts *opts)
 				le16_to_cpu(hs_epout_desc.wMaxPacketSize));
 
 	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
+	hs_epin_fback_desc.bEndpointAddress = fs_epin_fback_desc.bEndpointAddress;
 	hs_epin_desc.bEndpointAddress = fs_epin_desc.bEndpointAddress;
 
 	setup_descriptor(uac2_opts);
diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index e6d32c5..33c9288 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -43,6 +43,10 @@ struct uac_rtd_params {
 	unsigned int max_psize;	/* MaxPacketSize of endpoint */
 	struct uac_req *ureq;
 
+	struct usb_request *req_fback; /* Feedback endpoint request */
+	unsigned int ffback; /* Real frequency reported by feedback endpoint */
+	bool fb_ep_enabled; /* if the ep is enabled */
+
 	spinlock_t lock;
 };
 
@@ -76,6 +80,35 @@ struct snd_uac_chip {
 	.periods_min = MIN_PERIODS,
 };
 
+static void u_audio_set_fback_frequency(enum usb_device_speed speed,
+					unsigned int freq, void *buf)
+{
+	u32 ff = 0;
+
+	if (speed == USB_SPEED_FULL) {
+		/*
+		 * Full-speed feedback endpoints report frequency
+		 * in samples/microframe
+		 * Format is encoded in Q10.10 left-justified in the 24 bits,
+		 * so that it has a Q10.14 format.
+		 */
+		ff = DIV_ROUND_UP((freq << 14), 1000);
+	} else {
+		/*
+		 * High-speed feedback endpoints report frequency
+		 * in samples/microframe.
+		 * Format is encoded in Q12.13 fitted into four bytes so that
+		 * the binary point is located between the second and the third
+		 * byte fromat (that is Q16.16)
+		 *
+		 * Prevent integer overflow by calculating in Q12.13 fromat and
+		 * then shifting to Q16.16
+		 */
+		ff = DIV_ROUND_UP((freq << 13), (8*1000)) << 3;
+	}
+	*(__le32 *)buf = cpu_to_le32(ff);
+}
+
 static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
 {
 	unsigned int pending;
@@ -182,6 +215,36 @@ static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
 		dev_err(uac->card->dev, "%d Error!\n", __LINE__);
 }
 
+static void u_audio_iso_fback_complete(struct usb_ep *ep,
+				       struct usb_request *req)
+{
+	struct uac_rtd_params *prm = req->context;
+	struct snd_uac_chip *uac = prm->uac;
+	struct g_audio *audio_dev = uac->audio_dev;
+	int status = req->status;
+	unsigned long flags;
+
+	/* i/f shutting down */
+	if (!prm->fb_ep_enabled || req->status == -ESHUTDOWN)
+		return;
+
+	/*
+	 * We can't really do much about bad xfers.
+	 * Afterall, the ISOCH xfers could fail legitimately.
+	 */
+	if (status)
+		pr_debug("%s: iso_complete status(%d) %d/%d\n",
+			__func__, status, req->actual, req->length);
+
+	spin_lock_irqsave(&prm->lock, flags);
+	u_audio_set_fback_frequency(audio_dev->gadget->speed,
+				    prm->ffback, req->buf);
+	spin_unlock_irqrestore(&prm->lock, flags);
+
+	if (usb_ep_queue(ep, req, GFP_ATOMIC))
+		dev_err(uac->card->dev, "%d Error!\n", __LINE__);
+}
+
 static int uac_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
 {
 	struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
@@ -346,14 +409,33 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
 		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 }
 
+static inline void free_ep_fback(struct uac_rtd_params *prm, struct usb_ep *ep)
+{
+	struct snd_uac_chip *uac = prm->uac;
+
+	if (!prm->fb_ep_enabled)
+		return;
+
+	prm->fb_ep_enabled = false;
+
+	if (prm->req_fback) {
+		usb_ep_dequeue(ep, prm->req_fback);
+		kfree(prm->req_fback->buf);
+		usb_ep_free_request(ep, prm->req_fback);
+		prm->req_fback = NULL;
+	}
+
+	if (usb_ep_disable(ep))
+		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
+}
 
 int u_audio_start_capture(struct g_audio *audio_dev)
 {
 	struct snd_uac_chip *uac = audio_dev->uac;
 	struct usb_gadget *gadget = audio_dev->gadget;
 	struct device *dev = &gadget->dev;
-	struct usb_request *req;
-	struct usb_ep *ep;
+	struct usb_request *req, *req_fback;
+	struct usb_ep *ep, *ep_fback;
 	struct uac_rtd_params *prm;
 	struct uac_params *params = &audio_dev->params;
 	int req_len, i;
@@ -386,6 +468,42 @@ int u_audio_start_capture(struct g_audio *audio_dev)
 			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
 	}
 
+	ep_fback = audio_dev->in_ep_fback;
+	if (!ep_fback)
+		return 0;
+
+	/* Setup feedback endpoint */
+	config_ep_by_speed(gadget, &audio_dev->func, ep_fback);
+	prm->fb_ep_enabled = true;
+	usb_ep_enable(ep_fback);
+	req_len = ep_fback->maxpacket;
+
+	req_fback = usb_ep_alloc_request(ep_fback, GFP_ATOMIC);
+	if (req_fback == NULL)
+		return -ENOMEM;
+
+	prm->req_fback = req_fback;
+	req_fback->zero = 0;
+	req_fback->context = prm;
+	req_fback->length = req_len;
+	req_fback->complete = u_audio_iso_fback_complete;
+
+	req_fback->buf = kzalloc(req_len, GFP_ATOMIC);
+	if (!req_fback->buf)
+		return -ENOMEM;
+
+	/*
+	 * Configure the feedback endpoint's reported frequency.
+	 * Always start with original frequency since its deviation can't
+	 * be meauserd at start of playback
+	 */
+	prm->ffback = params->c_srate;
+	u_audio_set_fback_frequency(audio_dev->gadget->speed,
+				    prm->ffback, req_fback->buf);
+
+	if (usb_ep_queue(ep_fback, req_fback, GFP_ATOMIC))
+		dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(u_audio_start_capture);
@@ -394,6 +512,8 @@ void u_audio_stop_capture(struct g_audio *audio_dev)
 {
 	struct snd_uac_chip *uac = audio_dev->uac;
 
+	if (audio_dev->in_ep_fback)
+		free_ep_fback(&uac->c_prm, audio_dev->in_ep_fback);
 	free_ep(&uac->c_prm, audio_dev->out_ep);
 }
 EXPORT_SYMBOL_GPL(u_audio_stop_capture);
diff --git a/drivers/usb/gadget/function/u_audio.h b/drivers/usb/gadget/function/u_audio.h
index 5ea6b86..53e6baf 100644
--- a/drivers/usb/gadget/function/u_audio.h
+++ b/drivers/usb/gadget/function/u_audio.h
@@ -30,7 +30,10 @@ struct g_audio {
 	struct usb_gadget *gadget;
 
 	struct usb_ep *in_ep;
+
 	struct usb_ep *out_ep;
+	/* feedback IN endpoint corresponding to out_ep */
+	struct usb_ep *in_ep_fback;
 
 	/* Max packet size for all in_ep possible speeds */
 	unsigned int in_ep_maxpsize;
-- 
1.9.1