Re: [PATCH 1/2] USB: EHCI: Move sysfs related bits intoehci-sysfs.c

[Kirill Smelkov]

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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