usb: gadget: configure endpoint according to gadget speed

Add config_ep_by_speed() to configure the endpoint
according to the gadget speed.

Using this function will spare the FDs from handling
the endpoint chosen descriptor.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/composite.c

@@ -74,6 +74,91 @@ MODULE_PARM_DESC(iSerialNumber, "SerialNumber string");
 static char composite_manufacturer[50];
 
 /*-------------------------------------------------------------------------*/
+/**
+ * next_ep_desc() - advance to the next EP descriptor
+ * @t: currect pointer within descriptor array
+ *
+ * Return: next EP descriptor or NULL
+ *
+ * Iterate over @t until either EP descriptor found or
+ * NULL (that indicates end of list) encountered
+ */
+static struct usb_descriptor_header**
+next_ep_desc(struct usb_descriptor_header **t)
+{
+	for (; *t; t++) {
+		if ((*t)->bDescriptorType == USB_DT_ENDPOINT)
+			return t;
+	}
+	return NULL;
+}
+
+/*
+ * for_each_ep_desc()- iterate over endpoint descriptors in the
+ *		descriptors list
+ * @start:	pointer within descriptor array.
+ * @ep_desc:	endpoint descriptor to use as the loop cursor
+ */
+#define for_each_ep_desc(start, ep_desc) \
+	for (ep_desc = next_ep_desc(start); \
+	      ep_desc; ep_desc = next_ep_desc(ep_desc+1))
+
+/**
+ * config_ep_by_speed() - configures the given endpoint
+ * according to gadget speed.
+ * @g: pointer to the gadget
+ * @f: usb function
+ * @_ep: the endpoint to configure
+ *
+ * Return: error code, 0 on success
+ *
+ * This function chooses the right descriptors for a given
+ * endpoint according to gadget speed and saves it in the
+ * endpoint desc field. If the endpoint already has a descriptor
+ * assigned to it - overwrites it with currently corresponding
+ * descriptor. The endpoint maxpacket field is updated according
+ * to the chosen descriptor.
+ * Note: the supplied function should hold all the descriptors
+ * for supported speeds
+ */
+int config_ep_by_speed(struct usb_gadget *g,
+			struct usb_function *f,
+			struct usb_ep *_ep)
+{
+	struct usb_endpoint_descriptor *chosen_desc = NULL;
+	struct usb_descriptor_header **speed_desc = NULL;
+
+	struct usb_descriptor_header **d_spd; /* cursor for speed desc */
+
+	if (!g || !f || !_ep)
+		return -EIO;
+
+	/* select desired speed */
+	switch (g->speed) {
+	case USB_SPEED_HIGH:
+		if (gadget_is_dualspeed(g)) {
+			speed_desc = f->hs_descriptors;
+			break;
+		}
+		/* else: fall through */
+	default:
+		speed_desc = f->descriptors;
+	}
+	/* find descriptors */
+	for_each_ep_desc(speed_desc, d_spd) {
+		chosen_desc = (struct usb_endpoint_descriptor *)*d_spd;
+		if (chosen_desc->bEndpointAddress == _ep->address)
+			goto ep_found;
+	}
+	return -EIO;
+
+ep_found:
+	/* commit results */
+	_ep->maxpacket = le16_to_cpu(chosen_desc->wMaxPacketSize);
+	_ep->desc = chosen_desc;
+
+	return 0;
+}
 
 /**
  * usb_add_function() - add a function to a configuration