[PATCH v2] usb: gadget: f_uac1: add adaptive sync support for capture

[Charles Yi <be286@163.com>]

UAC1 has it's own freerunning clock and can update Host about
real clock frequency through feedback endpoint so Host can align
number of samples sent to the UAC1 to prevent overruns/underruns.

Change UAC1 driver to make it configurable through additional
'c_sync' configfs file.

Default remains 'asynchronous' with possibility to switch it
to 'adaptive'.

Signed-off-by: Charles Yi <be286@163.com>
---
 drivers/usb/gadget/function/f_uac1.c | 30 ++++++++++++++++++++++++++++
 drivers/usb/gadget/function/u_uac1.h |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/drivers/usb/gadget/function/f_uac1.c b/drivers/usb/gadget/function/f_uac1.c
index 6f0e1d803dc2..7a6fcb40bb46 100644
--- a/drivers/usb/gadget/function/f_uac1.c
+++ b/drivers/usb/gadget/function/f_uac1.c
@@ -33,6 +33,8 @@
 #define FUOUT_EN(_opts) ((_opts)->c_mute_present \
 			|| (_opts)->c_volume_present)
 
+#define EPOUT_FBACK_IN_EN(_opts) ((_opts)->c_sync == USB_ENDPOINT_SYNC_ASYNC)
+
 struct f_uac1 {
 	struct g_audio g_audio;
 	u8 ac_intf, as_in_intf, as_out_intf;
@@ -227,6 +229,16 @@ static struct uac_iso_endpoint_descriptor as_iso_out_desc = {
 	.wLockDelay =		cpu_to_le16(1),
 };
 
+static struct usb_endpoint_descriptor as_fback_ep_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 uac_format_type_i_discrete_descriptor as_in_type_i_desc = {
 	.bLength =		0, /* filled on rate setup */
 	.bDescriptorType =	USB_DT_CS_INTERFACE,
@@ -280,6 +292,7 @@ static struct usb_descriptor_header *f_audio_desc[] = {
 
 	(struct usb_descriptor_header *)&as_out_ep_desc,
 	(struct usb_descriptor_header *)&as_iso_out_desc,
+	(struct usb_descriptor_header *)&as_fback_ep_desc,
 
 	(struct usb_descriptor_header *)&as_in_interface_alt_0_desc,
 	(struct usb_descriptor_header *)&as_in_interface_alt_1_desc,
@@ -1107,6 +1120,9 @@ static void setup_descriptor(struct f_uac1_opts *opts)
 		f_audio_desc[i++] = USBDHDR(&as_out_type_i_desc);
 		f_audio_desc[i++] = USBDHDR(&as_out_ep_desc);
 		f_audio_desc[i++] = USBDHDR(&as_iso_out_desc);
+		if (EPOUT_FBACK_IN_EN(opts)) {
+			f_audio_desc[i++] = USBDHDR(&as_fback_ep_desc);
+		}
 	}
 	if (EPIN_EN(opts)) {
 		f_audio_desc[i++] = USBDHDR(&as_in_interface_alt_0_desc);
@@ -1317,6 +1333,12 @@ static int f_audio_bind(struct usb_configuration *c, struct usb_function *f)
 		ac_header_desc->baInterfaceNr[ba_iface_id++] = status;
 		uac1->as_out_intf = status;
 		uac1->as_out_alt = 0;
+
+		if (EPOUT_FBACK_IN_EN(audio_opts)) {
+			as_out_ep_desc.bmAttributes =
+			USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_SYNC_ASYNC;
+			as_out_interface_alt_1_desc.bNumEndpoints++;
+		}
 	}
 
 	if (EPIN_EN(audio_opts)) {
@@ -1354,6 +1376,12 @@ static int f_audio_bind(struct usb_configuration *c, struct usb_function *f)
 			goto err_free_fu;
 		audio->out_ep = ep;
 		audio->out_ep->desc = &as_out_ep_desc;
+		if (EPOUT_FBACK_IN_EN(audio_opts)) {
+			audio->in_ep_fback = usb_ep_autoconfig(gadget, &as_fback_ep_desc);
+			if (!audio->in_ep_fback) {
+				goto err_free_fu;
+			}
+		}
 	}
 
 	if (EPIN_EN(audio_opts)) {
@@ -1685,6 +1713,8 @@ static struct usb_function_instance *f_audio_alloc_inst(void)
 
 	opts->req_number = UAC1_DEF_REQ_NUM;
 
+	opts->c_sync = UAC1_DEF_CSYNC;
+
 	snprintf(opts->function_name, sizeof(opts->function_name), "AC Interface");
 
 	return &opts->func_inst;
diff --git a/drivers/usb/gadget/function/u_uac1.h b/drivers/usb/gadget/function/u_uac1.h
index f7a616760e31..c6e2271e8cdd 100644
--- a/drivers/usb/gadget/function/u_uac1.h
+++ b/drivers/usb/gadget/function/u_uac1.h
@@ -27,6 +27,7 @@
 #define UAC1_DEF_MAX_DB		0		/* 0 dB */
 #define UAC1_DEF_RES_DB		(1*256)	/* 1 dB */
 
+#define UAC1_DEF_CSYNC		USB_ENDPOINT_SYNC_ASYNC
 
 struct f_uac1_opts {
 	struct usb_function_instance	func_inst;
@@ -56,6 +57,7 @@ struct f_uac1_opts {
 
 	struct mutex			lock;
 	int				refcnt;
+	int				c_sync;
 };
 
 #endif /* __U_UAC1_H */
-- 
2.34.1