Messages in this thread | | | Date | Sun, 6 Mar 2011 00:53:34 -0700 | From | Grant Likely <> | Subject | Re: [PATCH 1/3] gpiolib: Add ability to get GPIO pin direction |
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On Tue, Feb 15, 2011 at 11:05:48AM -0600, Peter Tyser wrote: > > > Also, in most cases I'd think that the BIOS/U-Boot/firmware should have > > > configured the GPIO pins appropriately, which Linux should inherit in > > > general. Linux currently inherits GPIO states that were set in firmware > > > when a GPIO is requested, but it doesn't properly report those values > > > via sysfs - that's the only bug I'm trying to fix. > > > > Yes - however you can't fix it unless you are prepared to admit that the > > gpio has multiple states. At minimum you need to be able to report > > > > input/output/unknown/unavailable > > > > if you want to generalise it. Otherwise you don't solve the problem > > because you are asking a question that driver cannot answer correctly. > > As far as the "unknown" state, I can update the patch to have the logic: > + if (chip->get_direction) { > + /* chip->get_direction may sleep */ > + spin_unlock_irqrestore(&gpio_lock, flags); > + if (chip->get_direction(chip, gpio - chip->base) > 0) > + set_bit(FLAG_IS_OUT, &desc->flags); > + spin_lock_irqsave(&gpio_lock, flags); > + } else { > + set_bit(FLAG_IS_UNKNOWN, &desc->flags); > + } > > This would have the side effect of having nearly all GPIO drivers > default to an "unknown" direction until they implement the new > get_direction() function, which I think is an improvement over the > current system where they are all unconditionally shown as "input", > often incorrectly. Are you OK with this Grant?
Not really, no. Defaulting to "input" may be incorrect, but it is always safe, it it should only be a minor inconvenience to human users of the sysfs interface. Actual usage of a gpio pin must always be to explicitly set the direction before using a pin.
> Changing the logic to allow "unavailable" GPIO pins to be > requested/exported would require larger changes to the code, and > wouldn't provide much benefit without additional changes (eg an alt_func > feature). So I'd vote to not add support for "unavailable" pins in this > patch and rather wait until someone has a specific use for it, and add > it then.
Agreed.
g.
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