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[Qemu-devel] Re: Extending qemu_irq for reset signals

From: Blue Swirl
Subject: [Qemu-devel] Re: Extending qemu_irq for reset signals
Date: Wed, 15 Aug 2007 20:35:41 +0300

On 8/15/07, Paul Brook <address@hidden> wrote:
> On Wednesday 15 August 2007, Paul Brook wrote:
> > > Okay, more explaining. This is the case where I'd want to use the
> > > signal: DMA controller ("upstream") can reset the slave device (ESP or
> > > Lance). DMA controller is created first and I also want to allocate
> > > reset signals at that point. Later when ESP is created, it should be
> > > possible to put ESP reset function and opaque data to the signal given
> > > but this is not possible with current API. Currently the DMA data
> > > would be passed to qemu_allocate_irqs.
> >
> > Ah, I see. The problem here is that you've got a cyclic dependency. For DMA
> > operations the ESP is in charge, so it makes sense to create the
> > subservient DMA device first. For the reset signals the DMA controller is
> > in charge so ideally you create the ESP device first. Because the DMA
> > interface is most complicated, it's probably takes precedence.
> >
> > I think you need to modify or use sparc32_dma_set_reset_data to take a
> > qemu_irq rather than a callback and opaque argument. Alternatively you can
> > move things around a bit and have the sun4m code do something similar. i.e.
> > the ESP and lance devices return the reset lines, then the sun4m code pokes
> > into the DMA device state.
> Oh, or you can pass a pointer to a qemu_irq from the DMA to the ESP and have
> the ESP poke its reset object in there that way.

That's what I had in mind. Should I just extend the API for example with
/* Change the callback function and/or data */
void qemu_irq_change(qemu_irq irq, qemu_irq_handler handler,
                     void *opaque);

There is a small problem that DMA may not assert the reset signal
before ESP gets the data in place. Usually devices perform reset when

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