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

[Li.Xiubo@xxxxxxxxxxxxx]

> 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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