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From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 4/5] Enable fw_cfg DMA interface for ARM
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To: Laszlo Ersek <lersek@redhat.com>
Cc: peter.maydell@linaro.org, Stefan Hajnoczi <stefanha@gmail.com>, "Gabriel L. Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, jordan.l.justen@intel.com, pbonzini@redhat.com, markmb@redhat.com

  Hi,

> > My hypothesis (which I guess I'm volunteering to verify, unless we
> > end up rejecting this immediately as a bad idea, for some reason that
> > I have missed), is that current functionality wouldn't change, given
> > the way existing callbacks work right now, and that we could run the
> > callback each time a blob is *selected*, rather than hooking into the
> > (dma/mmio/pio) read methods.
> 
> Callback executed on first read only sounds okay to me, callback
> executed on selection... hm... don't like it. :)

Care to explain why?

I think callback on selection would be better.  Interface is more clear
then, I don't like read having different behavior depending on hidden
state (current offset).  And in practice selection and read will always
be called together, so there shouldn't be a difference in practice ...

cheers,
  Gerd