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Date: Wed, 20 Oct 2010 01:02:13 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH v5 00/14] pcie port switch emulators
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To: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: skandasa@cisco.com, etmartin@cisco.com, qemu-devel@nongnu.org, wexu2@cisco.com

On Wed, Oct 20, 2010 at 07:55:56AM +0900, Isaku Yamahata wrote:
> On Wed, Oct 20, 2010 at 12:40:49AM +0200, Michael S. Tsirkin wrote:
> 
> > I think I suggested once a good way to implement this:
> > 
> > - always make the bits w1c
> > - after config write:
> >   if MHR is enabled, and you see that error log is not empty and that bit is 0,
> >   this means that someone has written 1b.
> >   so pop the first error from the log, and set bit to 1 if it's not empty.
> > 
> > This way we only touch w1c mask on setup, no tricky range checks.
> > Anything wrong with this approach?
> 
> Basically okay. 
> Without the range checks, we need to restore the old value to the register
> if 1b isn't written to the bit of the first error.
> Probably you prefer restoring it mostly always than the range check.

Well that would be consistent with how we handle config cycles
in the rest of the code. We had a lot of tricky range checking code
and we killed it all in favor of making operations idempotent so
they are safe to redo on each config cycle.

-- 
MST