linux-kernel - Re: [PATCH] of/irq: lookup 'interrupts-extended' property first

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Date:	Wed, 6 Aug 2014 17:24:12 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Tim Bird <tbird20d@...il.com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of/irq: lookup 'interrupts-extended' property first

On Wed, Aug 6, 2014 at 4:50 PM, Tim Bird <tbird20d@...il.com> wrote:
> On Wed, Aug 6, 2014 at 1:12 PM, Brian Norris
> <computersforpeace@...il.com> wrote:
>> On Wed, Aug 06, 2014 at 01:42:08PM -0500, Rob Herring wrote:
>>> On Wed, Aug 6, 2014 at 11:54 AM, Brian Norris <computersforpeace@...il.com> wrote:
>>> > On Thu, Jul 31, 2014 at 11:00:01AM -0700, Florian Fainelli wrote:
>>> > I think it is important that a device tree provide some flexibility on
>>> > kernel versions. We only invented 'interrupts-extended' in Linux 3.13,
>>> > so it's easy to have device trees that could work only on 3.13+.
>>> >
>>> > Typically, we might say that new features require new kernels, but this
>>> > is a very basic piece of the DT infrastructure. In our case, we have
>>> > hardware whose basic features can be supported by a single interrupt
>>> > parent, and so we used the 'interrupts' property pre-3.13. But when we
>>> > want to add some power management features, there's an additional
>>> > interrupt parent. Under the current DT binding, we have to switch over
>>> > to using 'interrupts-extended' exclusively, and thus we must have a
>>> > completely new DTB for >=3.13, and this DTB no longer works with the old
>>> > kernels.
>>>
>>> "Must have" to enable the new features?
>>
>> Yes. The new feature requires an additional interrupt parent, and so it
>> requires interrupts-extended.
>
> Hold on there.  What about interrupt-map?  That was the traditional DT
> feature for
> supporting multi-parented interrupts.  Why couldn't the feature have been added
> using that instead of interrupts-extended?

It could have, but interrupts-extended is much more simple to express
for the simple case of a device's interrupts routed to more than one
parent.

> I know interrupts-extended is preferred, but has interrupt-map support been
> removed from recent kernels?  I'm a bit confused.

They are all still supported. It's just a question of order of parsing
if you have find both styles.

Rob
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