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authorGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-04-10 13:45:27 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-04-10 13:45:27 +0200
commitc8d1bc12c7986c166bd3504213d9df2bc11ad7d6 (patch)
tree9882ae7d9eb103c73029050d62232cd83328be52 /include
parentb7a4abb67416aa07cd65446dd39e64525ccfe8e5 (diff)
parentbbc78c07a51f6fd29c227b1220a9016e585358ba (diff)
Merge tag 'usb-for-v4.1-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb into usb-testing
Felipe writes: usb: generic resume timeout for v4.1 This part 2 pull request contains only the patches which make sure everybody on linux uses the same resume timeout value. Signed-off-by: Felipe Balbi <balbi@ti.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/usb.h26
1 files changed, 26 insertions, 0 deletions
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 7ee1b5c3b4cb..447fe29b55b4 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -205,6 +205,32 @@ void usb_put_intf(struct usb_interface *intf);
#define USB_MAXINTERFACES 32
#define USB_MAXIADS (USB_MAXINTERFACES/2)
+/*
+ * USB Resume Timer: Every Host controller driver should drive the resume
+ * signalling on the bus for the amount of time defined by this macro.
+ *
+ * That way we will have a 'stable' behavior among all HCDs supported by Linux.
+ *
+ * Note that the USB Specification states we should drive resume for *at least*
+ * 20 ms, but it doesn't give an upper bound. This creates two possible
+ * situations which we want to avoid:
+ *
+ * (a) sometimes an msleep(20) might expire slightly before 20 ms, which causes
+ * us to fail USB Electrical Tests, thus failing Certification
+ *
+ * (b) Some (many) devices actually need more than 20 ms of resume signalling,
+ * and while we can argue that's against the USB Specification, we don't have
+ * control over which devices a certification laboratory will be using for
+ * certification. If CertLab uses a device which was tested against Windows and
+ * that happens to have relaxed resume signalling rules, we might fall into
+ * situations where we fail interoperability and electrical tests.
+ *
+ * In order to avoid both conditions, we're using a 40 ms resume timeout, which
+ * should cope with both LPJ calibration errors and devices not following every
+ * detail of the USB Specification.
+ */
+#define USB_RESUME_TIMEOUT 40 /* ms */
+
/**
* struct usb_interface_cache - long-term representation of a device interface
* @num_altsetting: number of altsettings defined.