[RFC PATCH 06/10] hwspinlock: OMAP4: Add spinlock support in DT

[Ohad Ben-Cohen]

On Wed, Aug 24, 2011 at 4:09 PM, Benoit Cousson <b-cousson at ti.com> wrote:
> Add a device-tree node for the spinlock.
> Remove the static device build code if CONFIG_OF
> is set.
> Update the hwspinlock driver to use the of_match method.
> Add the information in Documentation/devicetree.
>
> Signed-off-by: Benoit Cousson <b-cousson at ti.com>
> Cc: Grant Likely <grant.likely at secretlab.ca>
> Cc: Ohad Ben-Cohen <ohad at wizery.com>
> ---
...
> +               spinlock {
> +                       compatible = "ti,omap-spinlock";
> +                       hwmods = "spinlock";
> +               };

This seem to satisfy the current hwspinlock driver, but I'm wondering
about an issue which was discussed awhile ago by Arnd and Mathieu:

Hwspinlock devices provide system-wide hardware locks that are used by
remote processors that have no other way to achieve synchronization.

For that to work, each physical lock must have a system-wide unique id
number that all processors are familiar with, otherwise they can't
possibly assume they're using the same hardware lock.

Usually SoC have a single hwspinlock device, which provides several
hardware spinlocks, and in this case, the locks can be trivially
numbered 0 to (num-of-locks - 1).

In case boards have several hwspinlocks devices (each of which
providing numerous hardware spinlocks) a different base id should be
used for each hwspinlock device (they can't all use 0 as a starting
id!).

While this is certainly not common, it's just plain wrong for the
hwspinlock driver to silently use 0 as a base id whenever it is probed
with a device (and by that implicitly assume there will always be only
one device).

So we need to couple an hwspinlock device with a base id (which is
trivially zero when there's only a single hwspinlock device). This can
be easily achieved today using platform data, which boards will use to
set a different base id for each of the hwspinlock devices they have
(i'll send a patch demonstrating this soon), but I'm wondering how to
specify this hwspinlock-specific data with DT: is there an existing
binding we can use for this ? or should we create something like a
"baseid" one especially for the hwspinlock driver ?

> +#if defined(CONFIG_OF)
> +static const struct of_device_id spinlock_match[] = {
> +       {.compatible = "ti,omap-spinlock", },
> +       {},
> +}

you're missing a semicolon there (yeah I actually tried to build this ;)