linux-kernel - Re: [PATCHv7 1/4] pwm: Add Freescale FTM PWM driver support

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Date:	Tue, 17 Dec 2013 14:22:48 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Tomasz Figa <tomasz.figa@...il.com>,
	Xiubo Li <Li.Xiubo@...escale.com>, mark.rutland@....com,
	s.hauer@...gutronix.de, galak@...eaurora.org,
	swarren@...dotorg.org, t.figa@...sung.com, grant.likely@...aro.org,
	matt.porter@...aro.org, rob@...dley.net, ian.campbell@...rix.com,
	pawel.moll@....com, rob.herring@...xeda.com,
	linux-arm-kernel@...ts.infradead.org, linux-pwm@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, Alison Wang <b18965@...escale.com>,
	Jingchang Lu <b35083@...escale.com>
Subject: Re: [PATCHv7 1/4] pwm: Add Freescale FTM PWM driver support

On Tue, Dec 17, 2013 at 01:04:35PM +0000, Russell King - ARM Linux wrote:
> On Tue, Dec 17, 2013 at 01:54:35PM +0100, Tomasz Figa wrote:
> > On Tuesday 17 of December 2013 13:45:06 Thierry Reding wrote:
> > > I fail to see how that would eliminate the problem with the types. That
> > > said I don't actually see sparse complaining about any type mismatches.
> > > That's probably because the various macros implicitly cast to u32.
> > 
> > Well, in BE variant you would read the register using __raw_readl() into
> > a __be32 and then get an u32 from be32_to_cpu() and return it. Similarly
> > for writes
> 
> __raw_readl() returns a u32, so you'll get a warning trying to assign a
> u32 to a __be32.

If sparse doesn't complain about the original code here, does that mean
we have a bug that should be fixed?

> We do have ioread32() and ioread32be() which do the appropriate conversion,
> as well as the write versions too.  They both include the barrier if you're
> overly concerned about that.

A few years ago GregKH commented in response to a patch that ioread*()
weren't supposed to be used for memory-mapped only devices. The original
purpose apparently was to allow drivers to work with both I/O and
memory-mapped devices.

Thierry

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