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

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Message-ID: <20160422112239.GF10606@leverpostej>
Date:	Fri, 22 Apr 2016 12:22:39 +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 Fri, Apr 22, 2016 at 12:12:57PM +0100, Jon Hunter wrote:
> 
> On 22/04/16 11:00, Mark Rutland wrote:
> > On Wed, Apr 20, 2016 at 12:03:56PM +0100, Jon Hunter wrote:
> >> The Tegra AGIC interrupt controller is compatible with the ARM GIC-400
> >> interrupt controller.
> > 
> > The cover letter says it _is_ a GIC-400, just used in a slightly unusual
> > manner (i.e. not directly connected to CPUs).
> 
> Correct.
> 
> >> The Tegra AGIC requires two clocks, namely the
> >> "ape" (functional) and "apb2ape" (interface) clocks, to operate. Add
> >> the compatible string and clock information for the AGIC to the GIC
> >> device-tree binding documentation.
> > 
> > The GIC-400 spec only describes "CLK" (which is what I imagine "ape" is.
> > There isn't an APB clock described, and the manual seems to show GIC-400
> > directly connected to AXI rather than APB, so that doesn't seem to even
> > be the usual "apb_pclk".
> > 
> > Is there some wrapper logic around a GIC-400 to giove it an APB
> > interface? Or am I misudnerstanding the spec?
> 
> Looking at the Tegra documentation what we have is ...
> 
> APB --> AXI switch --> AGIC (GIC400)
> 
> I am not sure how such a switch would typically be modeled in DT but we
> need the apb clock to interface to the GIC registers. I am not sure if
> something like simple-pm-bus is appropriate here.

I think we need some representation of that AXI switch in the DT;
whether simple-pm-bus is appropriate is another question. We probably
need a specific compatible string / binding regardless.

Thanks,
Mark.

> 
> >> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> >> ---
> >>
> >> 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.

Thanks,
Mark.