Re: [PATCH 04/12] MIPS: GIC: Move MIPS_GIC_IRQ_BASE into platform irq.h

Andrew Bresticker
2014-09-02T22:22:31Z

On Mon, Sep 1, 2014 at 5:08 PM, Andrew Bresticker <abrestic@chromium.org> wrote:
> On Mon, Sep 1, 2014 at 1:34 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Sunday 31 August 2014 11:54:04 Andrew Bresticker wrote:
>>> On Sat, Aug 30, 2014 at 12:57 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>>> > On Friday 29 August 2014 15:14:31 Andrew Bresticker wrote:
>>> >> Define a generic MIPS_GIC_IRQ_BASE which is suitable for Malta and
>>> >> the upcoming Danube board in <mach-generic/irq.h>. Since Sead-3 is
>>> >> different and uses a MIPS_GIC_IRQ_BASE equal to the CPU IRQ base (0),
>>> >> define its MIPS_GIC_IRQ_BASE in <mach-sead3/irq.h>.
>>> >>
>>> >> Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
>>> >>
>>> >
>>> > Why do you actually have to hardwire an IRQ base? Can't you move
>>> > to the linear irqdomain code for DT based MIPS systems yet?
>>>
>>> Neither Malta nor SEAD-3 use device-tree for interrupts yet, so they
>>> still require a hard-coded IRQ base. For boards using device-tree, I
>>> stuck with a legacy IRQ domain as it allows most of the existing GIC
>>> irqchip code to be reused.
>>
>> I see. Note that we now have irq_domain_add_simple(), which should
>> do the right think in either case: use a legacy domain when a
>> nonzero base is provided for the old boards, but use the simple
>> domain when probed from DT without an irq base.
>>
>> This makes the latter case more memory efficient (it avoids
>> allocating the irq descriptors for every possibly but unused
>> IRQ number) and helps ensure that you don't accidentally rely
>> on hardcoded IRQ numbers for the DT based machines, which would
>> be considered a bug.
>
> Ah, ok. It looks like add_simple() is what I want then.

Actually, never mind. To re-use the existing GIC irqchip code I want
a legacy IRQ domain.