Re: [PATCH 08/12] irqdomain: Replace LEGACY mapping with LINEAR

[Grant Likely]

On Sat, Jun 16, 2012 at 12:01 AM, Benjamin Herrenschmidt
<benh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 2012-06-15 at 23:01 -0600, Grant Likely wrote:
>> The LEGACY mapping unnecessarily complicates the irqdomain code and
>> can easily be implemented with a linear mapping.  By ripping it out
>> and replacing it with the LINEAR mapping the object size of
>> irqdomain.c shrinks by about 330 bytes (ARMv7) which offsets the
>> additional allocation required by the linear map.  It also makes it
>> possible for current LEGACY map users to pre-allocate irq_descs for a
>> subset of the hwirqs and dynamically allocate the rest as needed.
>
> The point of legacy was to reserve 0...15, they could only be handed out
> to that controller, that guarantees that ancient crap x86 drivers with
> hard coded irq numbers would fail ... unless you have an x86-style
> chipset (PReP, some CHRP, ...).
>
> I'd like to keep that functionality a way or another.

The functionality is still entirely there; it's just implemented with
a linear map that gets populated with mappings to reserved irqs.
Everything *should* keep working correctly.

g.
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