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SubjectRe: [PATCH 01/10] irq: move some interrupt arch_* functions into struct irq_chip.
On Wed, 24 Mar 2010, Ian Campbell wrote:

> On Mon, 2010-03-22 at 10:19 +0000, Thomas Gleixner wrote:
> > On Sun, 21 Mar 2010, Yinghai Lu wrote:
> >
> > > From: Ian Campbell <ian.campbell@citrix.com>
> > >
> > > Move arch_init_copy_chip_data and arch_free_chip_data into function
> > > pointers in struct irq_chip since they operate on irq_desc->chip_data.
> >
> > Not sure about that. These functions are solely used by x86 and there
> > is really no need to generalize them.
>
> I thought the idea of struct irq_chip was to allow the potential for
> multiple IRQ controllers in a system? Given that it seems that struct
> irq_desc->chip_data ought to be available for use by whichever struct
> irq_chip is managing a given interrupt. At the moment this is not
> possible because we step around the abstraction using these arch_*
> methods.

Right, but you have exactly _ONE_ irq_chip associated to an irq_desc,
but that same irq_chip can be associated to several irq_descs. So
irq_desc->data is there to provide data for the irq_chip functions
depending on what irq they handle (e.g. base_address ...).

irq_desc->chip_data is set when the irq_chip is assigned to the
irq_desc.

So there is no point in having functions in irq_chip to set
irq_desc->chip_data.

Thanks,

tglx


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