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| -rw-r--r-- | include/linux/usb.h | 26 |
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. |