linux-kernel - Re: DT connectors, thoughts

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Date:	Thu, 21 Jul 2016 14:21:52 -0500
From:	Rob Herring <robh+dt@...nel.org>
To:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Cc:	David Gibson <david@...son.dropbear.id.au>,
	Frank Rowand <frowand.list@...il.com>,
	Stephen Boyd <stephen.boyd@...aro.org>,
	Mark Brown <broonie@...nel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Mark Rutland <mark.rutland@....com>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	Marek Vasut <marex@...x.de>, Wolfram Sang <wsa@...-dreams.de>,
	devicetree <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: Re: DT connectors, thoughts

On Thu, Jul 21, 2016 at 2:15 PM, Pantelis Antoniou
<pantelis.antoniou@...sulko.com> wrote:
> Hi Rob,
>
>> On Jul 21, 2016, at 22:09 , Rob Herring <robh+dt@...nel.org> wrote:
>>
>> On Thu, Jul 21, 2016 at 9:14 AM, Pantelis Antoniou
>> <pantelis.antoniou@...sulko.com> wrote:
>>> Hi David,
>>>
>>>> On Jul 21, 2016, at 16:42 , David Gibson <david@...son.dropbear.id.au> wrote:
>>>>
>>>> On Wed, Jul 20, 2016 at 11:59:44PM +0300, Pantelis Antoniou wrote:
>>>>> Hi David,
>>>>>
>>>>> Spent some time looking at this, and it looks like it’s going to the right direction.
>>>>>
>>>>> Comments inline.
>>>>>
>>>>>> On Jul 18, 2016, at 17:20 , David Gibson <david@...son.dropbear.id.au> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Here's some of my thoughts on how a connector format for the DT could
>>>>>> be done.  Sorry it's taken longer than I hoped - I've been pretty
>>>>>> swamped in my day job.
>>>>>>
>>>>>> This is pretty early thoughts, but gives an outline of the approach I
>>>>>> prefer.
>>
>> [...]
>>
>>>>>>            i2c: i2c@... {
>>>>>>            };
>>>>>>            intc: intc@... {
>>>>>>                    #interrupt-cells = <2>;
>>>>>>            };
>>>>>>    };
>>>>>>
>>>>>>    connectors {
>>>>>>            widget1 {
>>>>>>                    compatible = "foo,widget-socket";
>>>>>>                    w1_irqs: irqs {
>>>>>>                            interrupt-controller;
>>>>>>                            #address-cells = <0>;
>>>>>>                            #interrupt-cells = <1>;
>>>>>>                            interrupt-map-mask = <0xffffffff>;
>>>>>>                            interrupt-map = <
>>>>>>                                    0 &intc 7 0
>>>>>>                                    1 &intc 8 0
>>>>>>> ;
>>>>>>                    };
>>>>>
>>>>> This is fine. We need an interrupt controller node.
>>>>
>>>> Actually I think we only need an interrupt nexus, not an interrupt
>>>> controller (in IEEE1275 terminology).  (An interrupt controller would
>>>> generally require it's own driver, to ack/mask irqs, whereas this just
>>>> demonstrates the routing to an existing interrupt controller).  Which
>>>> makes that example slightly incorrect (it shouldn't have the
>>>> interrupt-controller property).
>>>
>>> Hmm, as far as I can tell we only have a concept of an interrupt controller
>>> in the kernel. An interrupt nexus is something new. We should get by without
>>> a driver but hacking the interrupt lookup path at DT.
>>
>> Interrupt nexus is the interrupt-map property which is fully
>> supported. I'd expect we'll end up with a gpio nexus (i.e. gpio-map)
>> for connector gpios, too.
>>
>
> Is interrupt-map enough to cover all our cases? On all the cases that I see it
> used is in the context of PCI or some sort of bus.

I think it should be. IIRC, one of the ARM, Ltd. boards uses it in a
non-PCI context.

> Is the example above well defined? As far as I can tell interrupt-controller is not
> needed.

interrupt-controller should actually be dropped as that is supposed to
be mutually exclusive to interrupt-map, but I think the kernel doesn't
care.

Rob