usb: add helper to extract bits 12:11 of wMaxPacketSize

According to USB Specification 2.0 table 9-4,
wMaxPacketSize is a bitfield. Endpoint's maxpacket
is laid out in bits 10:0. For high-speed,
high-bandwidth isochronous endpoints, bits 12:11
contain a multiplier to tell us how many
transactions we want to try per uframe.

This means that if we want an isochronous endpoint
to issue 3 transfers of 1024 bytes per uframe,
wMaxPacketSize should contain the value:

	1024 | (2 << 11)

or 5120 (0x1400). In order to make Host and
Peripheral controller drivers' life easier, we're
adding a helper which returns bits 12:11. Note that
no care is made WRT to checking endpoint type and
gadget's speed. That's left for drivers to handle.

Signed-off-by: Felipe Balbi <[email protected]>

Author: Felipe Balbi

include/uapi/linux/usb/ch9.h

@@ -423,6 +423,11 @@ struct usb_endpoint_descriptor {
 #define USB_ENDPOINT_XFER_INT		3
 #define USB_ENDPOINT_MAX_ADJUSTABLE	0x80
 
+#define USB_EP_MAXP_MULT_SHIFT	11
+#define USB_EP_MAXP_MULT_MASK	(3 << USB_EP_MAXP_MULT_SHIFT)
+#define USB_EP_MAXP_MULT(m) \
+	(((m) & USB_EP_MAXP_MULT_MASK) >> USB_EP_MAXP_MULT_SHIFT)
+
 /* The USB 3.0 spec redefines bits 5:4 of bmAttributes as interrupt ep type. */
 #define USB_ENDPOINT_INTRTYPE		0x30
 #define USB_ENDPOINT_INTR_PERIODIC	(0 << 4)
@@ -630,6 +635,20 @@ static inline int usb_endpoint_maxp(const struct usb_endpoint_descriptor *epd)
 	return __le16_to_cpu(epd->wMaxPacketSize);
 }
 
+/**
+ * usb_endpoint_maxp_mult - get endpoint's transactional opportunities
+ * @epd: endpoint to be checked
+ *
+ * Return @epd's wMaxPacketSize[12:11] + 1
+ */
+static inline int
+usb_endpoint_maxp_mult(const struct usb_endpoint_descriptor *epd)
+{
+	int maxp = __le16_to_cpu(epd->wMaxPacketSize);
+
+	return USB_EP_MAXP_MULT(maxp) + 1;
+}
+
 static inline int usb_endpoint_interrupt_type(
 		const struct usb_endpoint_descriptor *epd)
 {