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

[Grant Likely <grant.likely@secretlab.ca>]

On Thu, Jul 07, 2011 at 10:15:31PM +0530, Nori, Sekhar wrote:
> 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@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.

We *absolutely* still need the helper function for the complex
settings, but for the non-complex ones, I'd rather just directly
access the structure.  The kerneldoc documentation of the structure
can and should be explicit about what the caller is allowed to do.

g.