On Thu, May 24, 2018 at 12:39 AM, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, May 23, 2018 at 10:03:55AM -0400, Alan Stern wrote: >> On Wed, 23 May 2018, Nicolas Boichat wrote: >> >> > The "old" enumeration scheme is considerably faster (it takes >> > ~294ms instead of ~439ms to get the descriptor). >> > >> > It is currently only possible to use the old scheme globally >> > (/sys/module/usbcore/parameters/old_scheme_first), which is not >> > desirable as the new scheme was introduced to increase compatibility >> > with more devices. >> > >> > However, in our case, we care about time-to-active for a specific >> > USB device (which we make the firmware for), on a specific port >> > (that is pogo-pin based: not a standard USB port). This new >> > sysfs option makes it possible to use the old scheme on a single >> > port only. >> > >> > Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx> >> > --- >> > >> > There are other "quirks" that we could add to reduce further >> > enumeration time (e.g. reduce USB debounce time, reduce TRSTRCY >> > to 10ms instead of 50ms as used currently), but the logic is quite >> > similar, so it'd be good to have this reviewed first. >> >> I'm not opposed to the idea in principle, although I don't like your >> implementation because it breaks the original old_scheme_first >> parameter. I don't think it breaks the original parameter? I mean, /sys/module/usbcore/parameters/old_scheme_first is still a global default, while bit 0 of /sys/bus/usb/devices/x/y/z/quirks becomes a port-specific override. >> Let's see what some other people think. >> >> Yours is a rather special case, because you know exactly what device >> will be attached to a specific port. Still, I can see that sort of >> thing happening in constrained and special-purpose settings. >> >> How do you arrange to set the new quirk before the device is >> discovered? > > Yeah, this last question is what I had when looking at this. Or does it > not matter at first boot and only matters for wake-up? It does not matter on boot, we have plenty of time to enumerate the device. We use USB (auto-)suspend and remote wake, so no re-enumeration there either. It only matters on unplug/replug where the device needs to be re-enumerated. Somewhere in an init script, we would do this (we know in advance that usb1 port2 is the bus/port where we have our pogo-pin USB interface, so we can hard-code the path): echo 1 > /sys/bus/usb/devices/usb1/1-0:1.0/usb1-port2/quirks We could try to add ACPI support (just like connect_type), but we don't strictly need it for our application. Thanks, -- 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
