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

[Jon Hunter <jonathanh@nvidia.com>]

On 27/04/16 18:38, Mark Rutland wrote:
> On Wed, Apr 27, 2016 at 04:34:53PM +0100, Jon Hunter wrote:
>>
>> On 22/04/16 12:22, Mark Rutland wrote:
>>
>> [snip]
>>
>>>>>> I am not sure if it will be popular to add Tegra specific clock names
>>>>>> to the GIC DT docs. However, in that case, then possibly the only
>>>>>> alternative is to move the Tegra AGIC driver into its own file and
>>>>>> expose the GIC APIs for it to use. Then we could add our own DT doc
>>>>>> for the Tegra AGIC as well (based upon the ARM GIC).
>>>>>
>>>>> The clock-names don't seem right to me, as they sound like provide names
>>>>> or global clock line names rather than consumer-side names ("clk" and
>>>>> "apb_pclk").
>>>>
>>>> Yes that would be fine with me.
>>>
>>> Ok; if we model the apb_pclk as owned by the AXI switch (which it is),
>>> then there's no change for the GIC binding, short of the additional
>>> compatible string as an extension of "arm,gic-400", as we already model
>>> that clock in the GIC-400 binding.
>>
>> I have been re-working this based upon the feedback received. In the GIC
>> driver we have the following definitions ...
>>
>>  IRQCHIP_DECLARE(gic_400, "arm,gic-400", gic_of_init);
>>  IRQCHIP_DECLARE(arm11mp_gic, "arm,arm11mp-gic", gic_of_init);
>>  IRQCHIP_DECLARE(arm1176jzf_dc_gic, "arm,arm1176jzf-devchip-gic", gic_of_init);
>>  IRQCHIP_DECLARE(cortex_a15_gic, "arm,cortex-a15-gic", gic_of_init);
>>  IRQCHIP_DECLARE(cortex_a9_gic, "arm,cortex-a9-gic", gic_of_init);
>>  IRQCHIP_DECLARE(cortex_a7_gic, "arm,cortex-a7-gic", gic_of_init);
>>  IRQCHIP_DECLARE(msm_8660_qgic, "qcom,msm-8660-qgic", gic_of_init);
>>  IRQCHIP_DECLARE(msm_qgic2, "qcom,msm-qgic2", gic_of_init);
>>  IRQCHIP_DECLARE(pl390, "arm,pl390", gic_of_init);
>>
>>
>> If I have something like the following in my dts ...
>>
>> 	agic: interrupt-controller@702f9000 {
>> 		compatible = "nvidia,tegra210-agic", "arm,gic-400";
>> 		...
>> 	};
>>
>> The problem with this is that it tries to register the interrupt controller
>> early during of_irq_init() before the platform driver has chance to
>> initialise it.
> 
> Probe order strikes again...
> 
>> To avoid this I got rid of the "nvidia,tegra210-agic" string and added
>> the following for the platform driver ...
>>
>> static const struct of_device_id gic_match[] = {
>>        { .compatible = "arm,arm11mp-gic-pm",    .data = &arm11mp_gic_data   },
>>        { .compatible = "arm,cortex-a15-gic-pm", .data = &cortexa15_gic_data },
>>        { .compatible = "arm,cortex-a9-gic-pm",  .data = &cortexa9_gic_data  },
>>        { .compatible = "arm,gic400-pm",         .data = &gic400_data        },
>>        { .compatible = "arm,pl390-pm",          .data = &pl390_data         },
>>        {},
>> };
>>
>> It is not ideal as now we have a *-pm variant of each compatible string :-(
> 
> Yeah, that's a non-starter. :(

That is what I feared. Understood.

>> Another option would be to add some code in gic_of_init() to check for the
>> presence of a "clocks" node in the DT binding and bail out of the early 
>> initialisation if found but may be that is a bit of a hack.
> 
> I fear that someone may validly have a clocks property in their root GIC
> node, at which point things would fall apart. I was under the impression
> this was the case for some Renesas boards (though I didn't find an
> example in tree).
> 
> So I suspect that using the clocks property in that way isn't going to
> work out well.
> 
>> Mark, what are your thoughts on this?
> 
> Collectively: "aargh", "oh no".

Yes, exactly :-(

> We could instead explicitly match "nvidia,tegra210-agic", bailing out if
> we see that. Otherwise, if we can't handle it like a GIC-400, then we
> can just drop the GIC-400 compatible string from the fallback list.

Would it also be a none-starter to have "arm,gic-pm" instead of
"nvidia,tegra210-agic"? At this point it is not really specific to tegra
any more and so I was hoping to get rid of that. For example, ...

	compatible = "arm,gic-pm", "arm,gic-400";

Cheers
Jon