[PATCH] gpio: Add Altera GPIO driver

[Tobias Klauser]

On 2012-03-12 at 17:04:18 +0100, Grant Likely <grant.likely at secretlab.ca> wrote:
> On Mon,  6 Feb 2012 18:59:02 +0100, Tobias Klauser <tklauser at distanz.ch> wrote:
> > This driver supports the Altera PIO core.
> > 
> > Signed-off-by: Thomas Chou <thomas at wytron.com.tw>
> > Signed-off-by: Tobias Klauser <tklauser at distanz.ch>
> > ---
> > This driver was submitted already about a year ago by Thomas, was
> > adjusted by him according to some remarks made by Grant and was then
> > included in the -mm tree [1] for some time but dropped again
> > (couldn't find out when and why exactly).
> > 
> > [0] http://article.gmane.org/gmane.linux.drivers.devicetree/4231
> > [1] http://article.gmane.org/gmane.linux.kernel.commits.mm/65119
> > 
> > So this is a new attempt towards getting this driver into mainline
> > from the nios2 tree. The following changes have been made atop the
> > version submitted by Thomas:
> > 
> > - Changed driver name to new naming convention
> > - Usage of of_property_read_u32 in the probe function
> 
> This looks like a pretty generic memory-mapped gpio chip.  It should use the
> gpio-generic infrastructure instead of open-coding all of the accessor hooks.

Thanks a lot for the hint.

I'm trying to figure out how this could work together with
of_mm_gpio_chip which we use in the driver. Both bgpio_chip and
of_mm_gpio_chip contain a struct gpio_chip, so I suppose we can only
"be" either one of them in our driver? What would be the prefered way to
do this?

Also as we need to register the driver from platform specific setup code
(in the out-of-mainline nios2 port only atm) very early on, we don't
have a struct platform_device or struct device available which we would
need to pass to bgpio_init. What's the best way to solve this?

And another issue I came across: gpio-generic only seems to support
8/16/32/64 bit wide GPIO registers. The Altera GPIO controller can have
from 1 to 32 bits per register depending on the configuration in the
FPGA (though it will still always be a 32bit register). In bgpio_init
the size passed is checked for being a number of 2 and the number then
written to the bits member. What would be the best way to still
determine the "real" number of GPIOs available in the driver then?

Thanks
Tobias