Re: [patch 04/16] genirq: Introduce irq_chip.irq_compose_msi_msg() to support stacked irqchip

[Thomas Gleixner]

On Tue, 18 Nov 2014, Yun Wu (Abel) wrote:
> On 2014/11/12 21:42, Thomas Gleixner wrote:
> > +int irq_chip_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> > +{
> > +	struct irq_data *pos = NULL;
> > +
> > +#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
> > +	for (; data; data = data->parent_data)
> > +#endif
> > +		if (data->chip && data->chip->irq_compose_msi_msg)
> > +			pos = data;
> > +	if (!pos)
> > +		return -ENOSYS;
> > +
> > +	pos->chip->irq_compose_msi_msg(pos, msg);
> > +
> > +	return 0;
> > +}
> 
> Adding message composing routine to struct irq_chip is OK to me, and it should
> be because it is interrupt controllers' duty to compose messages (so that they
> can parse the messages correctly without any pre-defined rules that endpoint
> devices absolutely need not to know).
> However a problem comes out when deciding which parameters should be passed to
> this routine. A message can associate with multiple interrupts, which makes me
> think composing messages for each interrupt is not that appropriate. And we
> can take a look at the new routine irq_chip_compose_msi_msg(). It is called by
> msi_domain_activate() which will be called by irq_domain_activate_irq() in
> irq_startup() for each interrupt descriptor, result in composing a message for
> each interrupt, right? (Unless requiring a judge on the parameter @data when
> implementing the irq_compose_msi_msg() callback that only compose message for
> the first entry of that message. But I really don't like that...)

No, that's not correct. You are looking at some random stale version
of this. The current state of affairs is in 

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq/irqdomain

See also https://lkml.org/lkml/2014/11/17/764

In activate we write the message, which is the right point to do so.

Thanks,

	tglx
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