linux-kernel - Re: [PATCH 2/2] regmap: Make regmap-mmio usable from different contexts

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Message-ID: <519E38ED.7090202@wwwdotorg.org>
Date:	Thu, 23 May 2013 09:42:37 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	Mark Brown <broonie@...nel.org>,
	Davide Ciminaghi <ciminaghi@...dd.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] regmap: Make regmap-mmio usable from different contexts

On 05/23/2013 07:06 AM, Lars-Peter Clausen wrote:
> regmap-mmio uses a spinlock with spin_lock() and spin_unlock() for locking.
> Which means in order to avoid race conditions the lock always needs to be taken
> from the same context.

I'm not really sure what this means. I assume contexts are
atomic-vs-nonatomic? If so, spinlocks should work fine for this, right?

I guess the core of the issue is that you want to replace spin_lock()
with spin_lock_irqsave(). I'd like to see that explicitly described in
the commit description, if that is the core aspect of this change.

Re: the other comments about the API change: I think this can be done
non-invasively:

static void regmap_lock_spinlock(void *__map)
{
	struct regmap *map = __map;
	unsigned long local_flags;

	spin_lock_irqsave(&map->spinlock, local_flags);
	/*
	 * Here, we have the lock locked, so we own the flags,
	 * and can write to them.
	 */
	map->spinlock_flags = local_flags;
}

static void regmap_unlock_spinlock(void *__map, unsigned long *flags)
{
	struct regmap *map = __map;
	spin_unlock_irqrestore(&map->spinlock, map->spinlock_flags);
}

... and obviously add a spinlock_flags field to struct regmap (perhaps
start unioning the mutex and spinlock data fields there if you want to
save space).
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