Re: [alsa-devel] [PATCH] ASoC: mediatek: Use current HW pointer for pointer callback

[Mark Brown <broonie@kernel.org>]

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On Thu, Dec 03, 2015 at 12:07:26PM +0100, Takashi Iwai wrote:
> Mark Brown wrote:
> > On Thu, Dec 03, 2015 at 10:41:38AM +0100, Takashi Iwai wrote:

> > > While reading this patch, I wondered how regmap can be used safely in
> > > an irq-disabled context.  Mark, do we have any API for that?

> > We can use user supplied locks or spin_lock_irqsave().

> I meant how to guarantee to make regmap_read() working in an already
> spin-locked context, typically in an irq handler?  regmap_read()
> involves with the regcache and it may invoke kmalloc().

I know that's what you meant - that should be done by preallocating the
cache (which can be done with defaults) and providing your own lock
if there's a spinlock already held (since we use _irqsave() which IIRC
isn't nestable).  We can also use GFP_ATOMIC for some of the allocations
in reasonable use cases but it's not in general supported.

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