linux-kernel - Re: [PATCH v7 1/4] Documentation: dt: add common bindings for hwspinlock

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Date:	Thu, 15 Jan 2015 13:55:56 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Suman Anna <s-anna@...com>
Cc:	Ohad Ben-Cohen <ohad@...ery.com>,
	Kumar Gala <galak@...eaurora.org>,
	Bjorn Andersson <bjorn@...o.se>,
	Josh Cartwright <joshc@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v7 1/4] Documentation: dt: add common bindings for
 hwspinlock

On Thu, Jan 15, 2015 at 01:52:01PM +0000, Mark Rutland wrote:
> On Wed, Jan 14, 2015 at 08:58:18PM +0000, Suman Anna wrote:
> > This patch adds the generic common bindings used to represent
> > a hwlock device and use/request locks in a device-tree build.
> > 
> > All the platform-specific hwlock driver implementations need the
> > number of locks and associated base id for registering the locks
> > present within the device with the driver core. This base id
> > needs to be unique across multiple IP instances of a hwspinlock
> > device, so that each hwlock can be represented uniquely in a
> > system.
> > 
> > The number of locks is represented by 'hwlock-num-locks' property,
> > and the base id is represented by the 'hwlock-base-id' property.
> > The args specifier length is dependent on each vendor-specific
> > implementation and is represented through the '#hwlock-cells'
> > property. Client users need to use the property 'hwlocks' for
> > requesting specific lock(s).
> > 
> > Note that the document is named hwlock.txt deliberately to keep
> > it a bit more generic.
> > 
> > Cc: Rob Herring <robh+dt@...nel.org>
> > Signed-off-by: Suman Anna <s-anna@...com>
> > ---
> > v7: Revised binding info for hwlock-base-id, it is mandatory now
> > 
> >  .../devicetree/bindings/hwlock/hwlock.txt          | 55 ++++++++++++++++++++++
> >  1 file changed, 55 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/hwlock/hwlock.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/hwlock/hwlock.txt b/Documentation/devicetree/bindings/hwlock/hwlock.txt
> > new file mode 100644
> > index 000000000000..8de7aaf878f9
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwlock/hwlock.txt
> > @@ -0,0 +1,55 @@
> > +Generic hwlock bindings
> > +=======================
> > +
> > +Generic bindings that are common to all the hwlock platform specific driver
> > +implementations.
> > +
> > +The validity and need of these common properties may vary from one platform
> > +implementation to another. The platform specific bindings should explicitly
> > +state if an optional property is used. Please also look through the individual
> > +platform specific hwlock binding documentations for identifying the applicable
> > +properties.
> > +
> > +Common properties:
> > +- #hwlock-cells:	Specifies the number of cells needed to represent a
> > +			specific lock. This property is mandatory for all
> > +			platform implementations.
> > +- hwlock-num-locks:	Number of locks present in a hwlock device. This
> > +			property is needed on hwlock devices, where the number
> > +			of supported locks within a hwlock device cannot be
> > +			read from a register.
> > +- hwlock-base-id:	An unique base Id for the locks for a particular hwlock
> > +			device. This property is mandatory for all platform
> > +			implementations.
> 
> This property makes no sense. The ID encoded in the hwlock cells is
> relative to the instance (identified by phandle), not global. So the DT
> has no global ID space.
> 
> Why do you think you need this?

Having looked at the way this proeprty is used, NAK.

If you need to carve up a Linux-internal ID space, do that dynamically.
There is no need for this property.

Mark.
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