Re: [PATCH 3/3] IRQ: Maintain regs pointer globally rather than passing to IRQ handlers

Alan Stern
2006-10-03T18:03:15Z

[Most people removed from CC: since they probably aren't too interested in
this.]

On Mon, 2 Oct 2006, David Brownell wrote:

> On Monday 02 October 2006 2:34 pm, Alan Stern wrote:
> > On Mon, 2 Oct 2006, David Brownell wrote:
> >
> > > > > (*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking. It does
> > > > > something different depending on whether it's been supplied with a regs
> > > > > pointer or not.
> > >
> > > gaak! where did that come from? I'll be surprised if removing
> > > that causes any problem at all.
> >
> > Here's the statement in question:
> >
> > if (likely (regs && HC_IS_RUNNING(ohci_to_hcd(ohci)->state))) {
>
> Where as I said, removing the "regs &&" should be just fine.
> (Is the plan that David Howells re-issue that patch? If so, I'l
> expect e will just fix it that way...)
>
> > ...
> >
> > Notice another questionable use of hcd->state.
>
> Questionable in what way? When that code is called to clean up
> after driver death, that loop must be ignored ... every pending I/O
> can safely be scrubbed. That's the main point of that particular
> HC_IS_RUNNING() test. In other cases, it's essential not to touch
> DMA queue entries that the host controller is still using.

Questionable because changes to hcd->state aren't synchronized with the
driver. In this case it probably doesn't end up making any difference.

Removing "regs &&" might change other aspects too. For instance, does
this routine ever get called from a timer routine, where regs would
normally be NULL? In such situations removing "regs &&" would reverse
the sense of the test.

Alan Stern