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

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Message-ID: <lsq.1518322806.945573344@decadent.org.uk>
Date:   Sun, 11 Feb 2018 04:20:06 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Felipe Balbi" <felipe.balbi@...ux.intel.com>
Subject: [PATCH 3.2 72/79] usb: add helper to extract bits 12:11 of
 wMaxPacketSize

3.2.99-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Felipe Balbi <felipe.balbi@...ux.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@...ux.intel.com>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@...adent.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 */