linux-kernel - Re: [PATCH 04/10] hwspinlock/core/omap: fix id issues on multiple hwspinlock devices

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Date:	Wed, 21 Sep 2011 09:14:06 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 04/10] hwspinlock/core/omap: fix id issues on multiple
 hwspinlock devices

* Ohad Ben-Cohen <ohad@...ery.com> [110912 09:14]:
> 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 SoCs have a single hwspinlock device, which provides several
> hwspinlocks, and in this case, they 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 to just
> silently use 0 as a base id whenever the hwspinlock driver is probed.
> 
> This patch provides a hwspinlock_pdata structure, that boards can use
> to set a different base id for each of the hwspinlock devices they may
> have, and demonstrates how to use it with the omap hwspinlock driver
> (ultimately it will be DT which will supply this base_id information).
> 
> While we're at it, make sure the hwspinlock core prints an explicit
> error message in case an hwspinlock is registered with an id number
> that already exists; this will help users catch such base id issues.
> 
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Ohad Ben-Cohen <ohad@...ery.com>

Acked-by: Tony Lindgren <tony@...mide.com>
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