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

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Message-ID: <20151203145612.GF5727@sirena.org.uk>
Date:	Thu, 3 Dec 2015 14:56:12 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Koro Chen <koro.chen@...iatek.com>, lgirdwood@...il.com,
	alsa-devel@...a-project.org, srv_heupstream@...iatek.com,
	s.hauer@...gutronix.de, linux-kernel@...r.kernel.org,
	linux-mediatek@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [alsa-devel] [PATCH] ASoC: mediatek: Use current HW pointer for
 pointer callback

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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