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Subject[PATCH] [77/106] USB: xhci - fix math in xhci_get_endpoint_interval()
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Dmitry Torokhov <dtor@vmware.com>
commit dfa49c4ad120a784ef1ff0717168aa79f55a483a upstream.

When parsing exponent-expressed intervals we subtract 1 from the
value and then expect it to match with original + 1, which is
highly unlikely, and we end with frequent spew:

usb 3-4: ep 0x83 - rounding interval to 512 microframes

Also, parsing interval for fullspeed isochronous endpoints was
incorrect - according to USB spec they use exponent-based
intervals (but xHCI spec claims frame-based intervals). I trust
USB spec more, especially since USB core agrees with it.

This should be queued for stable kernels back to 2.6.31.

Reviewed-by: Micah Elizabeth Scott <micah@vmware.com>
Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
drivers/usb/host/xhci-mem.c | 85 ++++++++++++++++++++++++++++++++------------
1 file changed, 62 insertions(+), 23 deletions(-)
Index: linux-2.6.35.y/drivers/usb/host/xhci-mem.c
===================================================================
--- linux-2.6.35.y.orig/drivers/usb/host/xhci-mem.c
+++ linux-2.6.35.y/drivers/usb/host/xhci-mem.c
@@ -961,6 +961,47 @@ int xhci_setup_addressable_virt_dev(stru
return 0;
}

+/*
+ * Convert interval expressed as 2^(bInterval - 1) == interval into
+ * straight exponent value 2^n == interval.
+ *
+ */
+static unsigned int xhci_parse_exponent_interval(struct usb_device *udev,
+ struct usb_host_endpoint *ep)
+{
+ unsigned int interval;
+
+ interval = clamp_val(ep->desc.bInterval, 1, 16) - 1;
+ if (interval != ep->desc.bInterval - 1)
+ dev_warn(&udev->dev,
+ "ep %#x - rounding interval to %d microframes\n",
+ ep->desc.bEndpointAddress,
+ 1 << interval);
+
+ return interval;
+}
+
+/*
+ * Convert bInterval expressed in frames (in 1-255 range) to exponent of
+ * microframes, rounded down to nearest power of 2.
+ */
+static unsigned int xhci_parse_frame_interval(struct usb_device *udev,
+ struct usb_host_endpoint *ep)
+{
+ unsigned int interval;
+
+ interval = fls(8 * ep->desc.bInterval) - 1;
+ interval = clamp_val(interval, 3, 10);
+ if ((1 << interval) != 8 * ep->desc.bInterval)
+ dev_warn(&udev->dev,
+ "ep %#x - rounding interval to %d microframes, ep desc says %d microframes\n",
+ ep->desc.bEndpointAddress,
+ 1 << interval,
+ 8 * ep->desc.bInterval);
+
+ return interval;
+}
+
/* Return the polling or NAK interval.
*
* The polling interval is expressed in "microframes". If xHCI's Interval field
@@ -978,43 +1019,35 @@ static inline unsigned int xhci_get_endp
case USB_SPEED_HIGH:
/* Max NAK rate */
if (usb_endpoint_xfer_control(&ep->desc) ||
- usb_endpoint_xfer_bulk(&ep->desc))
+ usb_endpoint_xfer_bulk(&ep->desc)) {
interval = ep->desc.bInterval;
+ break;
+ }
/* Fall through - SS and HS isoc/int have same decoding */
case USB_SPEED_SUPER:
if (usb_endpoint_xfer_int(&ep->desc) ||
- usb_endpoint_xfer_isoc(&ep->desc)) {
- if (ep->desc.bInterval == 0)
- interval = 0;
- else
- interval = ep->desc.bInterval - 1;
- if (interval > 15)
- interval = 15;
- if (interval != ep->desc.bInterval + 1)
- dev_warn(&udev->dev, "ep %#x - rounding interval to %d microframes\n",
- ep->desc.bEndpointAddress, 1 << interval);
+ usb_endpoint_xfer_isoc(&ep->desc)) {
+ interval = xhci_parse_exponent_interval(udev, ep);
}
break;
/* Convert bInterval (in 1-255 frames) to microframes and round down to
* nearest power of 2.
*/
case USB_SPEED_FULL:
+ if (usb_endpoint_xfer_int(&ep->desc)) {
+ interval = xhci_parse_exponent_interval(udev, ep);
+ break;
+ }
+ /*
+ * Fall through for isochronous endpoint interval decoding
+ * since it uses the same rules as low speed interrupt
+ * endpoints.
+ */
case USB_SPEED_LOW:
if (usb_endpoint_xfer_int(&ep->desc) ||
- usb_endpoint_xfer_isoc(&ep->desc)) {
- interval = fls(8*ep->desc.bInterval) - 1;
- if (interval > 10)
- interval = 10;
- if (interval < 3)
- interval = 3;
- if ((1 << interval) != 8*ep->desc.bInterval)
- dev_warn(&udev->dev,
- "ep %#x - rounding interval"
- " to %d microframes, "
- "ep desc says %d microframes\n",
- ep->desc.bEndpointAddress,
- 1 << interval,
- 8*ep->desc.bInterval);
+ usb_endpoint_xfer_isoc(&ep->desc)) {
+
+ interval = xhci_parse_frame_interval(udev, ep);
}
break;
default:

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