Re: [Qemu-devel] [PATCH v2 2/2] hw/exynos4210_gic.c: Introduce n_in and n_out propeties.

[Evgeny Voevodin]

On 16.04.2012 15:01, Peter Maydell wrote:
> On 12 April 2012 09:13, Evgeny Voevodin<address@hidden>  wrote:
> > With these properties irq gate could be tuned to mux up to
> > QDEV_MAX_IRQ inputs and ouputs. Gate will group inputs
> > into groups of size n_in/n_out each.
> > @@ -420,14 +430,20 @@ static int exynos4210_irq_gate_init(SysBusDevice *dev)
> >      Exynos4210IRQGateState *s =
> >              FROM_SYSBUS(Exynos4210IRQGateState, dev);
> >
> > +    /* Gate will make each input group of size n_in / n_out */
> I think it would be useful to expand this comment to describe how the
> device uses its gpio_in and sysbus irq outputs. (This is necessary at
> the moment because we don't have the ability to have nicely named
> arrays of gpio inputs/outputs, so often the single gpio input array
> is arbitrarily divided up and you just have to document in a comment
> how it works; see for instance arm_gic.c and arm_mptimer.c. Something
> like:
>
> /* This device models a collection of OR gates. There are n_out
>   * separate gates, and output sysbus IRQ line N is the output of
>   * gate N. The input qdev gpio lines are the inputs to each gate
>   * in order:
>   *  [0.. n_in/n_out - 1] : inputs to gate 0
>   *  [n_in/n_out .. 2*n_in/n_out - 1] : inputs to gate 1
>   * and so on.
>   */

Ok.

> The other approach to consider would be to make each OR gate a separate
> device, and just instantiate N of them. That would probably look
> cleaner in the device implementation but be a little more code in
> exynos4210.c. I don't have a preference either way -- just a thought.

Do you mean to have each OR gate with only two inputs? Then if we want 
to mux n inputs into
one output, we'll have to place a number of gates after a gate output... 
As for me it's better
to have one configurable gate with multiple inputs.

> > +    if ((s->n_in % s->n_out) != 0) {
> > +        hw_error("n_in is not multiple of n_out in Irq Gate");
> "exynos4210.irq_gate: n_in must be a multiple of n_out".

Ok.

> -- PMM

Thanks!

--
Kind regards,
Evgeny Voevodin,
Leading Software Engineer,
ASWG, Moscow R&D center, Samsung Electronics
e-mail: address@hidden