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

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Message-ID: <CAL_JsqL2LZAooMk-V8+xeF2g6acZE21M+-OBRw8aEVa-5wVHuQ@mail.gmail.com>
Date:	Thu, 15 Jan 2015 08:42:23 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Mark Rutland <mark.rutland@....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 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.

Rob
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