usb: define a generic USB_RESUME_TIMEOUT macro (62f0342d) · Commits · 戴 / test

Every USB Host controller should use this new macro to define for how long resume signalling should be driven on the bus. Currently, almost every single USB controller is using a 20ms timeout for resume signalling. That's problematic for two reasons: a) sometimes that 20ms timer expires a little before 20ms, which makes us fail certification b) some (many) devices actually need more than 20ms resume signalling. Sure, in case of (b) we can state that the device is against the USB spec, but the fact is that we have no control over which device the certification lab will use. We also have no control over which host they will use. Most likely they'll be using a Windows PC which, again, we have no control over how that USB stack is written and how long resume signalling they are using. At the end of the day, we must make sure Linux passes electrical compliance when working as Host or as Device and currently we don't pass compliance as host because we're driving resume signallig for exactly 20ms and that confuses certification test setup resulting in Certification failure. Cc: <stable@vger.kernel.org> # v3.10+ Acked-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by:

Peter Chen <peter.chen@freescale.com> Signed-off-by:

Felipe Balbi <balbi@ti.com>

include/linux/usb.h

+26 −0

Original line number	Diff line number	Diff line
		@@ -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.

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