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

[Paul Brook <paul@codesourcery.com>]

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.

Paul