usb: gadget: uac2: add req_number as parameter

There are only two requests for uac2, it may not be enough at high
loading system which usb interrupt handler can't be serviced on
time, then the data will be lost since it is isoc transfer for audio.

In this patch, we introduce a parameter for the number for usb request,
and the user can override it if current number for request is not enough
for his/her use case.

Besides, update this parameter for legacy audio gadget and documentation.

Signed-off-by: Peter Chen <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

Documentation/usb/gadget-testing.txt

···
 	p_chmask - playback channel mask
 	p_srate - playback sampling rate
 	p_ssize - playback sample size (bytes)
+	req_number - the number of pre-allocated request for both capture
+		     and playback
 
 The attributes have sane default values.
 

drivers/usb/gadget/function/f_uac2.c

···
 
 #include "u_uac2.h"
 
-/* Keep everyone on toes */
-#define USB_XFERS	2
-
 /*
  * The driver implements a simple UAC_2 topology.
  * USB-OUT -> IT_1 -> OT_3 -> ALSA_Capture
···
 	size_t period_size;
 
 	unsigned max_psize;
-	struct uac2_req ureq[USB_XFERS];
+	struct uac2_req *ureq;
 
 	spinlock_t lock;
 };
···
 uac2_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
 {
 	struct snd_uac2_chip *uac2 = snd_pcm_substream_chip(substream);
+	struct audio_dev *agdev = uac2_to_agdev(uac2);
+	struct f_uac2_opts *uac2_opts = agdev_to_uac2_opts(agdev);
 	struct uac2_rtd_params *prm;
 	unsigned long flags;
 	int err = 0;
···
 
 	/* Clear buffer after Play stops */
 	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && !prm->ss)
-		memset(prm->rbuf, 0, prm->max_psize * USB_XFERS);
+		memset(prm->rbuf, 0, prm->max_psize * uac2_opts->req_number);
 
 	return err;
 }
···
 free_ep(struct uac2_rtd_params *prm, struct usb_ep *ep)
 {
 	struct snd_uac2_chip *uac2 = prm->uac2;
+	struct audio_dev *agdev = uac2_to_agdev(uac2);
+	struct f_uac2_opts *uac2_opts = agdev_to_uac2_opts(agdev);
 	int i;
 
 	if (!prm->ep_enabled)
···
 
 	prm->ep_enabled = false;
 
-	for (i = 0; i < USB_XFERS; i++) {
+	for (i = 0; i < uac2_opts->req_number; i++) {
 		if (prm->ureq[i].req) {
 			usb_ep_dequeue(ep, prm->ureq[i].req);
 			usb_ep_free_request(ep, prm->ureq[i].req);
···
 
 	prm = &agdev->uac2.c_prm;
 	prm->max_psize = hs_epout_desc.wMaxPacketSize;
-	prm->rbuf = kzalloc(prm->max_psize * USB_XFERS, GFP_KERNEL);
+	prm->ureq = kcalloc(uac2_opts->req_number, sizeof(struct uac2_req),
+			GFP_KERNEL);
+	if (!prm->ureq) {
+		ret = -ENOMEM;
+		goto err_free_descs;
+	}
+	prm->rbuf = kcalloc(uac2_opts->req_number, prm->max_psize, GFP_KERNEL);
 	if (!prm->rbuf) {
 		prm->max_psize = 0;
 		ret = -ENOMEM;
···
 
 	prm = &agdev->uac2.p_prm;
 	prm->max_psize = hs_epin_desc.wMaxPacketSize;
-	prm->rbuf = kzalloc(prm->max_psize * USB_XFERS, GFP_KERNEL);
+	prm->ureq = kcalloc(uac2_opts->req_number, sizeof(struct uac2_req),
+			GFP_KERNEL);
+	if (!prm->ureq) {
+		ret = -ENOMEM;
+		goto err_free_descs;
+	}
+	prm->rbuf = kcalloc(uac2_opts->req_number, prm->max_psize, GFP_KERNEL);
 	if (!prm->rbuf) {
 		prm->max_psize = 0;
 		ret = -ENOMEM;
···
 	return 0;
 
 err_no_memory:
+	kfree(agdev->uac2.p_prm.ureq);
+	kfree(agdev->uac2.c_prm.ureq);
 	kfree(agdev->uac2.p_prm.rbuf);
 	kfree(agdev->uac2.c_prm.rbuf);
 err_free_descs:
···
 {
 	struct usb_composite_dev *cdev = fn->config->cdev;
 	struct audio_dev *agdev = func_to_agdev(fn);
+	struct f_uac2_opts *opts = agdev_to_uac2_opts(agdev);
 	struct snd_uac2_chip *uac2 = &agdev->uac2;
 	struct usb_gadget *gadget = cdev->gadget;
 	struct device *dev = &uac2->pdev.dev;
···
 		agdev->as_out_alt = alt;
 		req_len = prm->max_psize;
 	} else if (intf == agdev->as_in_intf) {
-		struct f_uac2_opts *opts = agdev_to_uac2_opts(agdev);
 		unsigned int factor, rate;
 		struct usb_endpoint_descriptor *ep_desc;
 
···
 	prm->ep_enabled = true;
 	usb_ep_enable(ep);
 
-	for (i = 0; i < USB_XFERS; i++) {
+	for (i = 0; i < opts->req_number; i++) {
 		if (!prm->ureq[i].req) {
 			req = usb_ep_alloc_request(ep, GFP_ATOMIC);
 			if (req == NULL)
···
 UAC2_ATTRIBUTE(c_chmask);
 UAC2_ATTRIBUTE(c_srate);
 UAC2_ATTRIBUTE(c_ssize);
+UAC2_ATTRIBUTE(req_number);
 
 static struct configfs_attribute *f_uac2_attrs[] = {
 	&f_uac2_opts_attr_p_chmask,
···
 	&f_uac2_opts_attr_c_chmask,
 	&f_uac2_opts_attr_c_srate,
 	&f_uac2_opts_attr_c_ssize,
+	&f_uac2_opts_attr_req_number,
 	NULL,
 };
 
···
 	opts->c_chmask = UAC2_DEF_CCHMASK;
 	opts->c_srate = UAC2_DEF_CSRATE;
 	opts->c_ssize = UAC2_DEF_CSSIZE;
+	opts->req_number = UAC2_DEF_REQ_NUM;
 	return &opts->func_inst;
 }
 
···
 
 	prm = &agdev->uac2.c_prm;
 	kfree(prm->rbuf);
+	kfree(prm->ureq);
 	usb_free_all_descriptors(f);
 }
 

drivers/usb/gadget/function/u_uac2.h

···
 #define UAC2_DEF_CCHMASK 0x3
 #define UAC2_DEF_CSRATE 64000
 #define UAC2_DEF_CSSIZE 2
+#define UAC2_DEF_REQ_NUM 2
 
 struct f_uac2_opts {
 	struct usb_function_instance	func_inst;
···
 	int				c_chmask;
 	int				c_srate;
 	int				c_ssize;
+	int				req_number;
 	bool				bound;
 
 	struct mutex			lock;

drivers/usb/gadget/legacy/audio.c

···
 	uac2_opts->c_chmask = c_chmask;
 	uac2_opts->c_srate = c_srate;
 	uac2_opts->c_ssize = c_ssize;
+	uac2_opts->req_number = UAC2_DEF_REQ_NUM;
 #else
 	uac1_opts = container_of(fi_uac1, struct f_uac1_opts, func_inst);
 	uac1_opts->fn_play = fn_play;