[RFC] Dummy GPIO driver for use with SPI

[Trent Piepho]

On Fri, 12 Dec 2008, Anton Vorontsov wrote:
> On Fri, Dec 12, 2008 at 11:59:13AM -0500, Steven A. Falco wrote:
>> What do you think about having a mechanism to specify that some
>> SPI slaves have a chip select, while others don't have to have a
>> chip select managed by the SPI subsystem?
>
> Um.. do you know that you can pass '0' as a GPIO?
>
> For example,
>
> spi-controller {
> 	gpios = <&pio1 1 0	/* cs0 */
> 		 0		/* cs1, no GPIO */
> 		 &pio2 2 0>;	/* cs2 */

It's ok the that middle specifier is only one word instead of three?  Seems
like "0 0 0" would be better, so all the specifiers are the same size.

> 		normal case;
> 	} else if (gpio == -EEXIST) {

Isn't EEXIST (pathname already exists) backward?  Seems like ENOENT would
be the right error code.  Except that's used for reading past the end...

Maybe a reading past the end should be EINVAL or EBADF?

Or return ENODEV for the 'hole' cell?  Or ENOLINK?

EEXIST is for trying to create something that already exists.  The 'hole'
is more like trying to follow a broken link or find something that doesn't
exist.