[RFC/RFT 1/2] gpio/basic_mmio: add support for enable register

[Nori, Sekhar]

Hi Grant,

On Thu, Jul 07, 2011 at 02:40:54, Grant Likely wrote:
> On Tue, Jul 05, 2011 at 04:15:44PM +1000, Ryan Mallon wrote:
> > On 05/07/11 15:10, Sekhar Nori wrote:
> > >Some GPIO controllers have an enable register
> > >which needs to be written to before a GPIO
> > >can be used.
> > >
> > >Add support for enabling the GPIO. At this
> > >time inverted logic for enabling the GPIO
> > >is not supported. This can be done by adding
> > >a disable register as and when a controller
> > >with this comes along.
> > >
> > >Signed-off-by: Sekhar Nori<nsekhar at ti.com>
> > >---
> > >
> > <snip>
> > 
> > >static int bgpio_setup_io(struct bgpio_chip *bgc,
> > >  			  void __iomem *dat,
> > >@@ -369,6 +401,7 @@ int __devinit bgpio_init(struct bgpio_chip *bgc,
> > >  			 void __iomem *clr,
> > >  			 void __iomem *dirout,
> > >  			 void __iomem *dirin,
> > >+			 void __iomem *en,
> > >  			 bool big_endian)
> > 
> > The arguments to this function are getting a bit unwieldy :-). Maybe
> > we need to introduce something like:
> > 
> > struct bgpio_chip_info {
> >     struct device *dev;
> >     unsigned long sz;
> >     void __iomem *dat;
> >     void __iomem *set;
> >     void __iomem *clr;
> >     void __iomem *dirout;
> >     void __iomem *dirin;
> >     void __iomem *en;
> >     bool big_endian;
> > };
> > 
> > and pass that to bgpio_init instead. It would have the added
> > benefits of making the drivers more readable and that
> > bgpio_chip_info structs in the drivers can probably be marked
> > __initdata also.
> 
> Or, what may be better is to make callers directly update the
> bgpio_chip structure.

I started implementing it this way, but felt that the bgpio_chip
structure also has many internal members (like the spinlock) and
this method will require users to spend quite a bit of time figuring
out which structure members they should initialize and which to leave
for bgpio_init() to do for them.

There is also the case of direction register which is set from
either dirout or dirin depending upon whether the logic is inverted
or not. The bgpio_chip however needs to deal with a single direction
register offset.

Considering these, I am getting inclined towards Ryan's suggestion.

Thoughts?

Thanks,
Sekhar