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

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Message-ID: <CAL_JsqK8BiffXgpQSig5EbV3FUW7EBOn9YjZGqOcUcEJiCJ0WA@mail.gmail.com>
Date:	Wed, 6 Aug 2014 13:42:08 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	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 11:54 AM, Brian Norris
<computersforpeace@...il.com> wrote:
> Hi Grant, et al,
>
> Can we get a comment here?
>
> On Thu, Jul 31, 2014 at 11:00:01AM -0700, Florian Fainelli wrote:
>> 2014-06-19 16:33 GMT-07:00 Florian Fainelli <f.fainelli@...il.com>:
>> > In case the Device Tree blob passed by the boot agent supplies both an
>> > 'interrupts-extended' and an 'interrupts' property in order to allow for
>> > older kernels to be usable, prefer the new-style 'interrupts-extended'
>> > property which convey a lot more information.
>> >
>> > This allows us to have bootloaders willingly maintaining backwards
>> > compatibility with older kernels without entirely deprecating the
>> > 'interrupts' property (although that is a clear violation of the binding
>> > specified at
>> > Documentation/devicetree/bindings/interrupt-controller/interrupts.txt)
>
> For the patch:
>
> Acked-by: Brian Norris <computersforpeace@...il.com>
>
> 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? I would expect a new kernel
and old dtb still works, right? That is the most important
compatibility issue to consider.

> How's that for DT stability?
>
> On the other hand, if we support this precedence concept, then a new DTB
> can provide both the 'interrupts-extended' and 'interrupts' properties,
> and thus be compatible with both pre-3.13 and
> post-<whenever-this-is-accepted> kernels.

Yes, this is what should be done. And I don't have any issue marking
this for stable if needed.

>> Any comments on this? Brian suggested that I update
>> interrupt-controller/interrupts.txt to specify the look up ordering
>> change as well.
>
> What do you think about the following DT binding doc update to accompany
> this change?

For both changes,

Acked-by: Rob Herring <robh@...nel.org>

Can you send a proper patch for the doc change or combine them.

Rob

>
> Signed-off-by: Brian Norris <computersforpeace@...il.com>
>
> diff --git a/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt b/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
> index 1486497a24c1..ce6a1a072028 100644
> --- a/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
> +++ b/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
> @@ -4,11 +4,13 @@ Specifying interrupt information for devices
>  1) Interrupt client nodes
>  -------------------------
>
> -Nodes that describe devices which generate interrupts must contain an either an
> -"interrupts" property or an "interrupts-extended" property. These properties
> -contain a list of interrupt specifiers, one per output interrupt. The format of
> -the interrupt specifier is determined by the interrupt controller to which the
> -interrupts are routed; see section 2 below for details.
> +Nodes that describe devices which generate interrupts must contain an
> +"interrupts" property, an "interrupts-extended" property, or both. If both are
> +present, the latter should take precedence; the former may be provided simply
> +for compatibility with software that does not recognize the latter. These
> +properties contain a list of interrupt specifiers, one per output interrupt. The
> +format of the interrupt specifier is determined by the interrupt controller to
> +which the interrupts are routed; see section 2 below for details.
>
>    Example:
>         interrupt-parent = <&intc1>;
--
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