On Fri, Dec 06, 2019 at 11:57:30AM +0800, Ikjoon Jang wrote: > On Thu, Dec 5, 2019 at 10:26 PM Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > On Thu, Dec 05, 2019 at 03:32:38PM +0800, Ikjoon Jang wrote: > > > On Wed, Dec 4, 2019 at 3:55 PM Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > > > But related to my question above, why do you need to do this during > > > > enumeration? Why not just set the lower interval value in the hub > > > > driver? > > > > > > Because I want device tree's bInterval to be checked against the same rules > > > defined in usb_parse_endpoint(). e.g. although hardware says its maximum > > > is 255, but the practical limit is still 0 to 16, so the code can > > > print warnings when bInterval from device node is too weird. > > > > But that could be handled refactoring the code in question or similar. > > Yes, that should be worked. I can't exactly figure out how to refactor > the code for now, but maybe parsed endpoint descriptors are being > checked with default hard wired bInterval value and after that > an overridden value should be checked again. > > Actually I don't care about the details of software policies. I just want > all devices to be handled in the same manner without any further > special treatments. I'd say you're indeed trying to give a specific device special treatment. ;) > > The fundamental problem here is that you're using devicetree, which is > > supposed to only describe the hardware, to encode policy which should be > > deferred to user space. > > The hub hardware has a default bInterval inside which is actually > adjustable. So I can think setting bInterval is to describe the hardware > rather than policy. No, the USB spec says bInterval is a maximum requested value and that the host is free to poll more often. And that's policy. > > So I think you need to figure out an interface that allows user space to > > set the polling interval for any hub at runtime instead. > > Changing the interval at runtime is an another way to solve the > power consumption problem, but it's not so easy. At least xhci needs > to restart an endpoint and no devices are changing the interval after > enumeration stage. The usb-hid driver actually supports configuring the polling rate for devices like mice and keyboards after enumeration (through a module parameter, but still). Unfortunately, the xhci driver does not yet support this and always uses the device maximum bInterval. A bug report for this was filed many years ago, perhaps it's time to address that (adding Mathias on CC): https://bugzilla.kernel.org/show_bug.cgi?id=82571 Johan
