[U-Boot] [PATCH] gpio: add driver for PCA9539 16-bit I2C gpio expander

[Peter Tyser <ptyser@xes-inc.com>]

<snip>

> > You could do the same thing to the U-Boot pca953x driver.
> > Eg at the top you could add:
> > #ifdef CONFIG_PCA953X_16BIT
> > #define NGPIO = 16
> > #else
> > #define NGPIO = 8
> > #endif
> 
> I have a small problem with this due to the fact that we have some
> designs here that use a pca9534 and a pca9539. Having a compile-time
> conditional like this means you can only support one or the other.
> Linux can handle this because it's actually got a structure that
> contains the 8 vs 16 whereas u-boot only has the address an no other
> information. Any suggestions on handling this would be welcome.

Some ideas:
- Do a series of byte reads and determine the number of GPIOs based on
mirroring of registers, or reads failing if they are past the "end" of
the device.  eg reading register 4 on a 8-bit device might fail, or wrap
around and return the same data as register 0.

- Make CONFIG_PCA953X_16BIT an array that lists which I2C address
support 16 bits, then use it to determine which devices are 8 vs 16 bits
dynamically.

- Convert the driver to be more intelligent.  eg add an interface like
pca953x_add_dev(u8 addr, u8 bits) which each board calls to add a device
to a list of devices maintained by the pca953x driver.  Eg in my board
code I'd do:
pca953x_add_dev(0x18, 8);
pca953x_add_dev(0x1c, 8);
pca953x_add_dev(0x1e, 8);
pca953x_add_dev(0x1f, 8);

Best,
Peter