[PATCH 3.2 72/79] usb: add helper to extract bits 12:11 of wMaxPacketSize

Ben Hutchings
2018-02-11T04:20:06Z

From: Felipe Balbi <felipe.balbi@linux.intel.com>

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>
---
include/linux/usb/ch9.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

--- 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(cons
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 */