Re: [PATCH] powerpc: mpc8xxx_gpio: Add ability to mask off unused GPIO pins

Hi Peter,

On Fri, Dec 04, 2009 at 01:43:40PM -0600, Peter Tyser wrote:

This change resolves 2 issues:
- Different chips have a different number of GPIO pins per controller.
  For example, the MPC8347 has 32, the P2020 16, and the mpc8572 8.
  Previously, the mpc8xxx_gpio driver assumed every chip had 32 GPIO
  pins which resulted in some processors reporting an incorrect 'ngpio'
  field in /sys.  Additionally, users could export and "use" 32 GPIO
  pins, although in reality only a subset of the 32 pins had any real
  functionality.

- Some boards don't utilize all available GPIO pins.  Previously,
  unused GPIO pins could still be exported and "used", even though the
  pins had no real functionality.  This is somewhat confusing to a user
  and also allow a user to do something "bad", like change an unused
  floating output into a floating input.

There are hundreds of other ways to screw things up.

Think of /dev/mem, you still able to change the registers.
Before changing any GPIO (whether it is a normal or reserved GPIO),
user has to consult with schematics/docs.

Adding a new "fsl,gpio-mask" device tree property allows a dts file to
accurately describe what GPIO pins are available for use on a given
board.

I don't see any real usage for this. If device tree specifies a wrong
gpio in the gpios = <> property, then it's a bug in the device tree
and should be fixed (or workarounded in the platform code).

If a user fiddles with unknown gpios via sysfs interface, then it's
user's problem.

FWIW, we don't have any masks for reserved IRQs.

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2