Subject: Re: polarity inversion on LS1021a
To: Alexander Stein <alexander.stein@systec-electronic.com>,
        Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Shawn Guo <shawnguo@kernel.org>
References: <67135504-72fb-ef7e-cac4-03331550a38d@prevas.dk>
 <2780635.GsDK2O7NgM@ws-stein>
From: Marc Zyngier <marc.zyngier@arm.com>
Organization: ARM Ltd
Message-ID: <4f27f4e1-f42c-e931-a31b-067bb62eed77@arm.com>
Date: Mon, 4 Dec 2017 15:37:20 +0000
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On 04/12/17 15:31, Alexander Stein wrote:
> Hi Rasmus,
> 
> On Monday, December 4, 2017, 4:11:06 PM CET Rasmus Villemoes wrote:
>> The LS1021A has a standard GIC-400, but allows inverting the polarity of
>> six external interrupt lines via a certain register, effectively
>> supporting IRQ_TYPE_LEVEL_LOW and IRQ_TYPE_EDGE_FALLING for those.
>>
>> I'm trying to figure out how one would add support for this. The patch
>> below works but is obviously just meant to help show what I mean, so
>> please don't comment on all the things that are wrong with it.
>>
>> It feels wrong to create a whole new irqchip driver copy-pasting the
>> entire irg-gic.c, but I can't figure out how and where one could hook
>> into the existing one. Any pointers on how to do this properly will be
>> greatly appreciated.
> 
> In my opinion a new irqchip is still required, but solely for modifying
> SCFG_INTPCR depending on IRQ_TYPE_*
> You would need to insert it as a cascading interrupt chip in device tree.
> You also need to protect accesses to this register using a spinlock.
> This is at least my idea how I would have done it, though never got time
> for it.
Almost. See my earlier reply. You just need a very minimal driver that
only takes care of the polarity thing. Nobody needs to see yet another
GIC driver...

	M.
-- 
Jazz is not dead. It just smells funny...