linux-kernel - Re: [PATCH] ASoC: fsl_asrc: Add reg_defaults for regmap to fix kernel dump

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Date:	Mon, 27 Oct 2014 21:26:26 -0700
From:	Nicolin Chen <nicoleotsuka@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	alsa-devel@...a-project.org
Subject: Re: [PATCH] ASoC: fsl_asrc: Add reg_defaults for regmap to fix
 kernel dump

On Tue, Oct 28, 2014 at 12:19:04AM +0000, Mark Brown wrote:
> On Fri, Oct 24, 2014 at 07:03:57PM -0700, Nicolin Chen wrote:
> > Kernel dump (WARN_ON) ocurred during system boot-up inside regmap_write():
> > 
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 47 at kernel/locking/lockdep.c:2744 lockdep_trace_alloc+0xe8/0x108()

> > Even though this may be a bug that should be fixed, I still try to send this
> > patch as a quick fix (work around) since it does no harm to assign default
> > values of every registers when using regcache.
> 
> It's not a bug, it's not reasonable to default allocations to atomic and
> we can't really tell what context we're in.  Anything used inside a
> heavily locked path should either have a default provided or arrange for
> a prior write to set up the cache.

I've a little trouble to understand the prior write over here. Inside my
probe() there's a register_init() call which has a set of regmap_write().
And then the first regmap_write() results the dump. Does that mean this
regmap_write() isn't prior write? If so, how should I do if not setting
default values here -- Some IPs may have default value 0 for registers.
And this would make reg_defaults tedious since there's nothing special
to assign.

And actually I remember I haven't seen any dump when I sent the initial
patch for the whole ASRC driver but it manifested last month. I thought
it might be a partially-merging issue and it would be fixed after merge
window's done.....

Thank you
Nicolin
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