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

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Date:	Wed, 18 Dec 2013 06:28:34 +0000
From:	"Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>
To:	Thierry Reding <thierry.reding@...il.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
CC:	"mark.rutland@....com" <mark.rutland@....com>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"t.figa@...sung.com" <t.figa@...sung.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"matt.porter@...aro.org" <matt.porter@...aro.org>,
	"rob@...dley.net" <rob@...dley.net>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Huan Wang <Huan.Wang@...escale.com>,
	"Jingchang Lu" <jingchang.lu@...escale.com>
Subject: RE: [PATCHv7 1/4] pwm: Add Freescale FTM PWM driver support


> On Tue, Dec 17, 2013 at 01:00:10PM +0100, Tomasz Figa wrote:
> > On Tuesday 17 of December 2013 11:51:36 Russell King - ARM Linux wrote:
> > > On Tue, Dec 17, 2013 at 12:10:22PM +0100, Thierry Reding wrote:
> > > > On Fri, Dec 13, 2013 at 04:57:04PM +0800, Xiubo Li wrote:
> > > > > +static inline u32 fsl_pwm_readl(struct fsl_pwm_chip *fpc,
> > > > > +		const void __iomem *addr)
> > > > > +{
> > > > > +	u32 val;
> > > > > +
> > > > > +	val = __raw_readl(addr);
> > > > > +
> > > > > +	if (likely(fpc->big_endian))
> > > >
> > > > The likely() probably isn't very useful in this case. But if you
> > > > want to keep it, it should at least be reversed, since
> > > > little-endian is actually the default (you have to specify the
> > > > big-endian property to activate the big endian mode).
> > > >
> > > > > +		val = be32_to_cpu(val);
> > > > > +	else
> > > > > +		val = le32_to_cpu(val);
> > >
> > > This will also cause sparse errors, because when sparse is enabled,
> > > these expect __le32 or __be32 arguments, not u32.
> >
> > My question is why can't you just create two sets of accessors, one
> > big endian and one little endian, add two function pointers to your
> > fsl_pwm_chip struct and let the driver set the to correct accessors in
> > probe?
> 
> I guess that would be one possibility.
>

Yes, that's one possibility.

If so, it must deference the function pointers and do the C stack push/pop stuff
every time when doing the accesses. For instance, but for some devices(USB, NET,
DMA..), we need to do many accesses every time in the frequent interrupt handler,
and I think the inline type functions will be more efficiency.

In LS-1 series platforms, there are many devices that need to do the same work like
this, and could these be moved to some global files ?


--
Xiubo
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