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 17:16:19 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Rob Herring <robh+dt@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	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 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.

Jon