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

commit 541b6fe63023f3059cf85d47ff2767a3e42a8e44 upstream.

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 <felipe.balbi@linux.intel.com>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/linux/usb/ch9.h b/include/linux/usb/ch9.h
index 046b1f4..68a3b10 100644 (file)
--- a/include/linux/usb/ch9.h
+++ b/include/linux/usb/ch9.h
@@ -390,6 +390,11 @@ 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)
+
 #define USB_ENDPOINT_SYNCTYPE          0x0c
 #define USB_ENDPOINT_SYNC_NONE         (0 << 2)
 #define USB_ENDPOINT_SYNC_ASYNC                (1 << 2)
@@ -592,6 +597,20 @@ 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;
+}
+
 /*-------------------------------------------------------------------------*/
 
 /* USB_DT_SS_ENDPOINT_COMP: SuperSpeed Endpoint Companion descriptor */