Re: [Xen-devel] [PATCH] PCI uart: fix boot hang, and second S3 resume inactive timer list corruption

[Tomasz Wroblewski <tomasz.wroblewski@xxxxxxxxxx>]

On 08/26/2013 03:52 PM, Jan Beulich wrote:
> > > > On 26.08.13 at 15:25, Tomasz Wroblewski<tomasz.wroblewski@xxxxxxxxxx>  wrote:
> > > Nevertheless, the approach of your patch in simply giving up
> > > the device (even if only termporarily) looks questionable to me
> > > We'd rather need to restore full access to it I would think. But
> > > yes, this hypervisor and Dom0 playing with the same device is
> > > sort of a gray area.
> > Restore ioport access at the start of poll routine (if not on) and
> > disable it again at the end (if was not on)? I might do that (if you
> > really prefer), but intuitively that seems more likely to produce side
> > effects in dom0 kernel than skipping a poll in xen
> As long as it's guaranteed to only be a poll (or a few of them) being
> affected, this is fine. But what if an interrupt is being used?
I'm probably missing something so can you elaborate on this? Probably 
not what you are asking, but ns16550_interrupt function currently 
doesn't hang when ioports are disabled as a byproduct of the     "while 
( !(ns_read_reg(uart, IIR) & IIR_NOINT) )" test in there, which already 
causes it to break out on 0xFF regs

> Jan

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