linux-kernel - Re: [PATCH V2 13/14] dt-bindings: arm-gic: Add documentation for Tegra210 AGIC

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Date:	Wed, 11 May 2016 11:30:18 -0500
From:	Rob Herring <robh+dt@...nel.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kevin Hilman <khilman@...nel.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 13/14] dt-bindings: arm-gic: Add documentation for
 Tegra210 AGIC

On Wed, May 11, 2016 at 11:16 AM, Jon Hunter <jonathanh@...dia.com> wrote:
>
> On 11/05/16 17:08, Jon Hunter wrote:
>> Hi Rob,
>>
>> On 11/05/16 16:51, Rob Herring wrote:
>>> On Sat, May 7, 2016 at 9:10 AM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>>> Hi Jon,
>>>>
>>>> On Fri, May 6, 2016 at 10:32 AM, Jon Hunter <jonathanh@...dia.com> wrote:
>>>>>> The "nvidia,tegra210-agic" string can be taken as describing any
>>>>>> Tegra-210 specific integration quirks, though I agree that's also not
>>>>>> fantastic for extending PM support beyond Tegra 210 and variants
>>>>>> thereof.
>>>>>>
>>>>>> So maybe the best approach is bailing out in the presence of clocks
>>>>>> and/or power domains after all, on the assumption that nothing today has
>>>>>> those properties, though I fear we may have problems with that later
>>>>>> down the line if/when people describe those for the root GIC to describe
>>>>>> those must be hogged, even if not explicitly managed.
>>>>>
>>>>> On further testing, by bailing out in the presence of clocks and/or
>>>>> power-domains, the problem I now see is that although the primary gic-400
>>>>> has been registered, we still try to probe it again later as it matches
>>>>> the platform driver. One way to avoid this would be ...
>>>>>
>>>>> diff --git a/drivers/of/irq.c b/drivers/of/irq.c
>>>>> index e7bfc175b8e1..631da7ad0dbf 100644
>>>>> --- a/drivers/of/irq.c
>>>>> +++ b/drivers/of/irq.c
>>>>> @@ -556,6 +556,8 @@ void __init of_irq_init(const struct of_device_id *matches)
>>>>>                          * its children can get processed in a subsequent pass.
>>>>>                          */
>>>>>                         list_add_tail(&desc->list, &intc_parent_list);
>>>>> +
>>>>> +                       of_node_set_flag(desc->dev, OF_POPULATED);
>>>>>                 }
>>>>
>>>> That sounds like the right thing to do to me...
>>>
>>> Seems fine to me, but it would be a problem since this is a global
>>> decision if you wanted to have some hand-off from an "early driver" to
>>> a platform driver. I guess setting the flag could move to drivers that
>>> need it although I don't think drivers should be touching the flags.
>>
>> Isn't this the other way around? Setting this flag means that I have
>> been populated and so don't bother creating a platform device for this
>> device as it isn't needed. A by-product if this, is that if we did
>> happen to have a platform driver for the irqchip that also has an early
>> driver, then the hand-off would never happen if the early init was
>> successful.
>>
>> The driver would still have to decide whether to hand-off and to do that
>> it would need to return an error from the early driver [0].
>>
>>>>> If this is not appropriate then I guess I will just need to use
>>>>> "tegra210-agic" for the compatibility flag.
>>>>
>>>> As I want this for plain gic-400, I'd be unhappy ;-)
>>>
>>> IMO, the plain gic-400 should not have these dependencies and you
>>> should use SoC specific compatible strings should you need to deal
>>> with this problem.
>>
>> It is fine for my case, but it does mean I cannot say ...
>>
>>       compatible = "tegra210-agic", "gic-400";
>>
>> ... because this will always match the early driver (unless we do
>> something like I have suggested above). So I would have ...
>
> Sorry this is wrong. The above will always match the early driver.
>
> The problem with the above compatibility string is that, if the platform
> driver matches "gic-400" then it will try to probe all gic-400s even if
> they have been initialised early and this is definitely not what we
> want. This could be solved by setting the OF_POPULATED flag.

A platform driver for just gic-400 is wrong IMO until we have platform
drivers for all interrupt controllers.

Another reason to set OF_POPULATED flag is we are needlessly creating
platform devices for irq controllers that will never have platform
drivers. So I'd go with that approach.

Rob