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

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Message-ID: <20140225111655.GA6855@e102568-lin.cambridge.arm.com>
Date:	Tue, 25 Feb 2014 11:16:56 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
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

Hi Stephen,

On Wed, Feb 19, 2014 at 12:20:43AM +0000, Stephen Boyd wrote:
> (Sorry, this discussion stalled due to merge window + life events)

Sorry for the delay in replying on my side too.

> On 01/17, Lorenzo Pieralisi wrote:
> > On Thu, Jan 16, 2014 at 07:26:17PM +0000, Stephen Boyd wrote:
> > > 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.
> > 
> > Ok, sorry, we are running around in circles here, basically you moved
> > the node to cpus according to reviews. I still think that treating cpus
> > as a device is not a great idea, even though I am in the same
> > position with C-states and probably will add C-state tables in the cpus
> > node.
> > 
> > http://comments.gmane.org/gmane.linux.power-management.general/41012
> > 
> > I just would like to see under cpus nodes and properties that apply to
> > all ARM systems, and avoid defining properties (eg interrupts) that
> > have different meanings for different ARM cores.
> > 
> > The question related to why the kernel should create a platform device
> > out of cpus is still open. I really do not want to block your series
> > for these simple issues but we have to make a decision and stick to that,
> > I am fine either way if we have a plan.
> > 
> 
> Do you just want a backup plan in case we don't make a platform
> device out of the cpus node? I believe we can always add code
> somewhere to create a platform device at runtime if we detect the
> cpus node has a compatible string equal to "qcom,krait". We could
> probably change this driver's module_init() to scan the DT for
> such a compatible string and create the platform device right
> there. If we get more than one interrupt in the cpus node we can
> add interrupt-names and then have software look for interrupts by
> name instead of number.

As I mentioned, I do not like the idea of adding compatible properties
just to force the kernel to create platform devices out of device tree
nodes. On top of that I would avoid adding a compatible property
to the cpus node (after all properties like enable-method are common for all
cpus but still duplicated), my only concern being backward compatibility
here (ie if we do that for interrupts, we should do that also for other
common cpu nodes properties, otherwise we have different rules for
different properties).

I think you can then add interrupts to cpu nodes ("qcom,krait" specific),
and as you mentioned create a platform device for that.

Thanks,
Lorenzo

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