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SubjectRe: [PATCH 00/53] dyn_array/nr_irqs/sparse_irq support v10
"Yinghai Lu" <yhlu.kernel@gmail.com> writes:

> On Thu, Aug 14, 2008 at 1:05 PM, Eric W. Biederman


>> What I wound up using in my tree is a little different.
>>
>> I introduced an opaque/empty structure: struct irq to be used in places
>> where we need pointers instead of an integer irq number in the interfaces.
>>
>> I have a version of the genirq api that works on struct irq instead of
>> unsigned int irq.
>>
>> I have functions:
>> struct irq * to_irq(unsigned int nr);
>> struct irq_desc *to_idesc(struct irq *);
>> unsigned int irq_nr(struct irq *irq);
>
> struct irq {
> unsigned int nr;
> struct irq_desc *idesc;
> }

I did:
struct irq_desc {
struct irq irq;
....
}
Then to_idesc is just a container_of call. Or simply a type cast but
that is rude.
Having nr be a field in struct irq is possibly valid.

When last we talked about the design Linus was emphatic that what gets
exposed to drivers be an opaque token. When I looked for 99%+ of the
arch code we can use that same opaque token. irq_desc is something
we don't really care about except in do_IRQ().

So I guess the truly important thing is that struct irq is not
ultimately available in a usable form to drivers.

We seem to give drivers access to everything when they include interrupt.h
So I'm not certain how strict we can succeed in being still is a good goal
to aim for.

>> Is there any reason why the migration path for architectures can not be:
>> Until they are converted:
>> #define NR_IRQS and use the irq_desc array.
>>
>> If they are just using a dynamically allocated array.
>> #define NR_IRQS nr_irqs
>>
>> Once we kill the array entirely.
>> #undef NR_IRQS or
>> #define NR_IRQS 0xfffff000
> why not use -1U here?

So that negative error codes continue not to be valid irqs.

In most places irq is an unsigned int so it may safely be used to index irq_desc.
In other paces people are sloppier and used a signed value so they can return
negative error values. create_irq() on x86 is one of those places. There
is also platform_get_irq. and possibly a few others.

Eric



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