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. > 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. > > 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. Thanks! > > Johan
