On Sat, 2016-12-03 at 10:05 +0100, Greg KH wrote: > On Fri, Dec 02, 2016 at 10:36:59PM -0800, Todd Brandt wrote: > > 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 remove the padding and use the spec minumums instead. > > > > The following patches do this by creating a struct which contains > > these three values, and allowing a module parameter to select between > > the current defaults and the spec minimums. The patch could be > > simplified to just use 3 defines, but I'm wary of making changes to > > core USB code without providing a backup and alot of community testing. > > I think these values have grown over the years due to bad devices being > reported. Look at the kernel logs for details. So we can not reduce > them by default. > > That being said, this is a nice change, but I really hate module > parameters. I could make it a global parameter like usb_spec_minimums=1, would that be better or just as bad? > > The first part is the core functionality. The second part provides a > > debug interface through sysfs to tweak the values directly at runtime. > > > > 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 > > Put this link in your first patch changelog please? ok > thanks, > > greg k-h -- 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
