linux-kernel - Re: [PATCH 4/9] ASoC: imx: Don't use {en,dis}able

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Message-ID: <CAKGA1bkiHj=zMJXSzoGp3fpLS3POnFXSV5y7sYYFAikqoUT9tQ@mail.gmail.com>
Date:	Mon, 6 Aug 2012 10:19:50 -0500
From:	Matt Sealey <matt@...esi-usa.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Russell King <linux@....linux.org.uk>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org,
	Sascha Hauer <kernel@...gutronix.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH 4/9] ASoC: imx: Don't use {en,dis}able_fiq() calls

On Sun, Aug 5, 2012 at 6:03 PM, Anton Vorontsov
<anton.vorontsov@...aro.org> wrote:
> The driver uses platform-specific mxc_set_irq_fiq() with the VIRQ cookie
> passed to it, so it's pretty clear that the driver is absolutely sure
> that the FIQ is routed via platform-specific IC, and that the cookie can
> be used to mask/unmask FIQs. So, let's switch to the genirq routines,
> since we're about to remove FIQ-specific variants.

I have a semi-related question about this;

Firstly, I was planning on (re-)submitting a patch for the
arch/arm/plat-mxc/ssi-fiq.S code which made it build in ARM mode
(since the code isn't Thumb compatible for various reasons) as it was
a blocker for a Thumb2-compiled kernel. Since the code was only needed
on ARM-capable processors it wouldn't cause a problem. Sascha signed
off on this a long while back and I've been testing it on all my
internal kernel versions, and I don't see any ill effects (that said I
don't have an i.MX28 or so to really verify it, I can't see why it
would not work). I realise this is redundant right now, anyway, since
it's only really enabled on imx_v4_v5 configs and they don't support
Thumb2 kernels anyway. What might be worth submitting is a switch to
add the ".arm" directive anyway simply for correctness since it could
never be compiled for Thumb anyway. We all know what gnu as is like.

Looking at it again on the back of these patches, I noticed the
ssi-fiq.S code is compiled in when SND_IMX_SOC is enabled - of course,
it's only needed in the kernel if SND_SOC_IMX_PCM_FIQ is enabled (the
code that uses the FIQ stuff is only compiled then) but here on the
Efika MX builds it's being built, and I noticed it when it broke my
build because of the above. I'm therefore going to submit a patch
which changes the ifdef SND_SOC_IMX to ifdef SND_SOC_IMX_PCM_FIQ so
it's not compiled in unless absolutely necessary. However, there was a
rumble that this code may disappear or be reworked in the future
making this also quite redundant. Since it's not in the
imx_v6_v7_defconfig anyway, I'm sure this only didn't get noticed
because nobody's building Thumb2 kernels and nobody is trying configs
with audio enabled anyway..

This begs the question, could there be something somewhere hidden deep
in the kernel that is enabled by default or in some config somewhere
that requires "select FIQ" in it's Kconfig entry, but isn't being
enabled? On i.MX the only thing turning it on is that code, but other
ARM arch enable it by default. Since things have been moved to more
generic routines I can't in my mind guarantee that such a patch would
be well tested here since I would be relying on symbols missing or
defines not there anymore.. I have no real way to ensure that it would
work on boards I don't have.

So, is the first patch (ssi-fiq.S .arm) worth it? I think the
SND_SOC_IMX_PCM_FIQ patch is worth it for v6_v7 systems anyway, but
maybe this should have been caught sooner, so should I update the
defconfig to enable some kind of audio bus support (Babbage has it in
the DT so is a needful thing for testing, I figure..)? And does anyone
forsee any problems with that option changing and the only "user" of
"FIQ" in the Kconfigs going away now all the FIQ-specific symbols went
away outside of the generic irq subsystem?

I will probably throw out all three today anyway, but I thought it
would make a good discussion anyway.

-- 
Matt Sealey <matt@...esi-usa.com>
Product Development Analyst, Genesi USA, Inc.
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