linux-kernel - Re: [PATCH 10/11] irqchip: bcm7120-l2: Extend driver to support 64+ bit controllers

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Date:	Wed, 29 Oct 2014 16:22:31 -0700
From:	Kevin Cernekee <cernekee@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Jonas Gorski <jogo@...nwrt.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>
Subject: Re: [PATCH 10/11] irqchip: bcm7120-l2: Extend driver to support 64+
 bit controllers

On Wed, Oct 29, 2014 at 12:53 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 28 October 2014 20:58:57 Kevin Cernekee wrote:
>> Most implementations of the bcm7120-l2 controller only have a single
>> 32-bit enable word + 32-bit status word.  But some instances have added
>> more enable/status pairs in order to support 64+ IRQs (which are all
>> ORed into one parent IRQ input).  Make the following changes to allow
>> the driver to support this:
>>
>>  - Extend DT bindings so that multiple words can be specified for the
>>    reg property, various masks, etc.
>>
>>  - Add loops to the probe/handle functions to deal with each word
>>    separately
>>
>>  - Allocate 1 generic-chip for every 32 IRQs, so we can still use the
>>    clr/set helper functions
>>
>>  - Update the documentation
>>
>> Signed-off-by: Kevin Cernekee <cernekee@...il.com>
>
> You should probably specify a 'big-endian' DT property for the driver
> to check. If you have both LE and BE versions of this device, we
> must make sure that we use the correct accessors.
>
> As long as we don't need to build a kernel that supports both (if
> I understand you correctly, the ARM SoCs use a LE instance of this
> device, while the MIPS SoCs use a BE version) you can still decide
> at compile-time which one you want, but please add the runtime check
> now, so if we ever get a new combination we can handle it at runtime
> with a more complex driver implementation.

Under discussion in the other thread...

> If I read your code right, you have decided to use one IRQ domain
> per register set, rather than one domain for all of them. I don't
> know which of the two ways is better here, but it would be good if
> you could explain in the patch description why you did it like this.

This uses one domain per bcm7120-l2 DT node.  If the DT node defines
multiple enable/status pairs (i.e. >=64 IRQs) then the driver will
create a single IRQ domain with 2+ generic chips.

Multiple generic chips are required because the generic-chip code can
only handle one enable/status register pair per instance.
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