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    SubjectRe: [PATCH 1/2] USB: EHCI: Move sysfs related bits into ehci-sysfs.c
    On Wed, Jun 29, 2011 at 01:35:04PM -0400, Alan Stern wrote:
    > On Wed, 29 Jun 2011, Kirill Smelkov wrote:
    >
    > > > Also, when decreasing the schedule limit, do you think it is really
    > > > necessary to check that the current allocation doesn't exceed the new
    > > > limit? I think it would be sufficient to apply the new limit just to
    > > > new bandwidth allocation requests. After all, this API is meant for
    > > > experts only.
    > >
    > > I think yes, it is needed. E.g. because there is this check in
    > > periodic_usecs():
    > >
    > > #ifdef DEBUG
    > > if (usecs > ehci->uframe_periodic_max)
    > > ehci_err (ehci, "uframe %d sched overrun: %d usecs\n",
    > > frame * 8 + uframe, usecs);
    > > #endif
    > > return usecs;
    > > }
    > >
    > > and periodic_usecs() is called in e.g. this chain:
    > >
    > > itd_submit
    > > iso_stream_schedule
    > > itd_slot_ok
    > > periodic_usecs
    > >
    > > and others.
    >
    > That won't matter unless DEBUG is defined.

    Yes, but still it would be good to always keep the invariant

    allocated <= uframe_periodic_max

    and that debug is there to catch when this breaks.


    > > I'd leave this check as is - to me it would be useful in debug mode to
    > > verify that we've not overallocated a period.
    > >
    > > Also, even if this knob would be useful only to experts, it would be
    > > better to put feedback onto the knob so that people could know whether
    > > thir request could be served or not.
    > >
    > > What do you think?
    >
    > Can you make that check conditional on DEBUG being set?

    Yes I can, but it seems to me we are starting to complicate the code.

    What's the problem with returning error on setting uframe_periodic_max <
    already allocated usb bandwith?


    Kirill


    P.S.

    The checking is not a priority for me here, so if you think it's better not
    to check or do it under #ifdef - let's do it. Though of course we all
    have our preferences :)


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