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

[Blue Swirl]

On 8/15/07, Blue Swirl <address@hidden> wrote:
> On 8/15/07, Paul Brook <address@hidden> wrote:
> > On Wednesday 15 August 2007, Blue Swirl wrote:
> > > 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);
> >
> > I'm not so keen on that. It breaks the nice property of having the IRQ lines
> > owned by the receiver. I was thinking something like:
> >
> > struct DMAState {
> >   qemu_irq device_reset;
> > };
> > qemu_irq *dma_init()
> > {
> >   struct DMAState * d = malloc();
> >   return &d->device_reset;
> > }
> >
> > void esp_init(qemu_irq *resetp)
> > {
> >   ESPState *d = malloc();
> >   *reset = *qemu_irq_alloc(d, 1);
> > }
> >
> > void sun4m_init()
> > {
> >   qemu_irq *p = dma_init();
> >   esp_init(p);
> > }
>
> Yes, that would work. I wasn't too happy about the change function either.
>

I implemented reset that way with qemu_irq, the result survives some
quick tests.

sparc32_reset.diff
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