linux-kernel - Re: [PATCH v5 2/4] devicetree: bindings: Document Krait CPU/L1 EDAC

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Date:	Thu, 16 Jan 2014 11:26:17 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 2/4] devicetree: bindings: Document Krait CPU/L1 EDAC

On 01/16, Lorenzo Pieralisi wrote:
> On Thu, Jan 16, 2014 at 06:05:05PM +0000, Stephen Boyd wrote:
> > On 01/16, Lorenzo Pieralisi wrote:
> > > Do we really want to do that ? I am not sure. A cpus node is supposed to
> > > be a container node, we should not define this binding just because we
> > > know the kernel creates a platform device for it then.
> > 
> > This is just copying more of the ePAPR spec into this document.
> > It just so happens that having a compatible field here allows a
> > platform device to be created. I don't see why that's a problem.
> 
> I do not see why you cannot define a node like pmu or arch-timer and stick
> a compatible property in there. cpus node does not represent a device, and
> must not be created as a platform device, that's my opinion.
> 

I had what you're suggesting before in the original revision of
this patch. Please take a look at the original patch series[1]. I
suppose it could be tweaked slightly to still have a cache node
for the L2 interrupt and the next-level-cache pointer from the
CPUs.

> What would you do for big.LITTLE systems ? We are going to create two
> cpus node because we need two platform devices ? I really think there
> must be a better way to implement this, but I will let DT maintainers
> make a decision.

There is no such thing as big.LITTLE for Krait, so this is not a
concern.

> 
> > > interrupts is a cpu node property and I think it should be kept as such.
> > > 
> > > I know it will be duplicated and I know you can't rely on a platform
> > > device for probing (since if I am not mistaken, removing a compatible
> > > string from cpus prevents its platform device creation), but that's an issue
> > > related to how the kernel works, you should not define DT bindings to solve
> > > that IMHO.
> > 
> > The interrupts property is also common for all cpus so it seems
> > fine to collapse the value down into a PPI specifier indicating
> > that all CPUs get the interrupt, similar to how we compress the
> > information about the compatible string.
> 
> I think it is nicer to create a device node (as I said, like a pmu or an
> arch-timer) and define interrupts there along with a proper compatible
> property. This would serve the same purpose without adding properties in
> the cpus node.
> 
> cpu-edac {
> 	compatible = "qcom,cpu-edac";
> 	interrupts = <...>;
> };

Yes, please see the original thread.

[1] https://lkml.org/lkml/2013/10/29/134

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