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Date: Tue, 2 Sep 2014 15:22:31 -0700
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Subject: Re: [PATCH 04/12] MIPS: GIC: Move MIPS_GIC_IRQ_BASE into platform irq.h
From: Andrew Bresticker <abrestic@chromium.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Ralf Baechle <ralf@linux-mips.org>, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>,
        Jeffrey Deans <jeffrey.deans@imgtec.com>,
        Markos Chandras <markos.chandras@imgtec.com>,
        Paul Burton <paul.burton@imgtec.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Linux-MIPS <linux-mips@linux-mips.org>,
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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.