The USB resume code in the kernel currently uses a set of hard coded delay values that are defined in the USB 2.0 spec. Specifically these three have the most effect on resume time: - tdrsmdn: resume signal time (20ms - infinity) usb 2.0 spec 7.1.7.7 - trsmrcy: resume recovery time (10ms) usb 2.0 spec 7.1.7.7 - trstrcy: reset recovery time (0ms - infinity) usb 2.0 spec 7.1.7.5 These values have been padded considerably in order to accomodate non-compliant devices. - tdrsmdn: resume signal time = 40ms - trsmrcy: resume recovery time = 10ms - trstrcy: reset recovery time = 50ms I propose that we provide a kernel parameter that sets the USB timing values to their spec minimums. The following patches do this by creating a global struct which contains these values. By default the values remain as they are now, but if usb_timing_minimum=1 is added to the kernel cmd line they're set to their minimums. This struct can be expanded over time to include other hardcoded values that have padding we can remove. I've created a blog entry on 01.org with some analyze_suspend test cases illustrating the benefits: - https://01.org/suspendresume/blogs/tebrandt/2016/usb-resume-optimization-using-spec-minimum-delays Todd Brandt (2): USB: add switch to turn off padding of resume time delays USB: usb resume time delay debug Documentation/admin-guide/kernel-parameters.txt | 7 +++ drivers/usb/core/hub.c | 12 ++--- drivers/usb/core/usb.c | 70 +++++++++++++++++++++++++ drivers/usb/dwc2/hcd.c | 2 +- drivers/usb/host/ehci-hcd.c | 4 +- drivers/usb/host/ehci-hub.c | 6 +-- drivers/usb/host/fotg210-hcd.c | 2 +- drivers/usb/host/isp116x-hcd.c | 2 +- drivers/usb/host/isp1362-hcd.c | 2 +- drivers/usb/host/ohci-hub.c | 2 +- drivers/usb/host/oxu210hp-hcd.c | 4 +- drivers/usb/host/r8a66597-hcd.c | 2 +- drivers/usb/host/sl811-hcd.c | 2 +- drivers/usb/host/uhci-hub.c | 6 +-- drivers/usb/host/xhci-hub.c | 6 +-- drivers/usb/host/xhci-ring.c | 2 +- drivers/usb/isp1760/isp1760-hcd.c | 2 +- drivers/usb/musb/musb_core.c | 6 +-- drivers/usb/musb/musb_virthub.c | 2 +- include/linux/usb.h | 23 +++++++- 20 files changed, 131 insertions(+), 33 deletions(-) -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
