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

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Date:	Fri, 16 Jan 2015 10:19:03 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Suman Anna <s-anna@...com>, 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 02:42:23PM +0000, Rob Herring wrote:
> On Thu, Jan 15, 2015 at 7:55 AM, Mark Rutland <mark.rutland@....com> wrote:
> > 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.
> 
> Better yet, don't create a Linux ID space for this. Everywhere we have
> one, we want to get rid of it.

Agreed. A completely opaque token / desc structure would prevent a lot
of potential abuse and save us from painful breakage.

Mark
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