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

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Date:	Wed, 27 Apr 2016 18:38:10 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Rob Herring <robh+dt@...nel.org>,
	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>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-tegra@...r.kernel.org, linux-omap@...r.kernel.org,
	devicetree@...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, 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@...f9000 {
> 		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. :(

> 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".

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.

Thanks,
Mark.