Messages in this thread | | | Date | Sun, 6 Mar 2011 23:52:53 -0700 | From | Grant Likely <> | Subject | Re: [PATCH v5 1/4] gpiolib: Add "unknown" direction support |
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On Sun, Mar 06, 2011 at 08:43:05PM -0600, Peter Tyser wrote: > > The thing about gpios is that how they are used is entirely dependant > > on what they are wired up to. There is no avoiding the fact that you > > *absolutely* must understand the usage model before even considering > > fiddling with a gpio (ignoring the "I wonder what this knob does" > > use-case such as when reverse engineer a board). So, while it is nice > > to have an 'unknown' state for sysfs to report, it is certainly not > > required. The model still remains that the pin direction must be set > > before (or at the same time as) reading/writing the pin. > > As is, even if someone knows about the GPIO wiring on their board, they > have to know Linux has a "rule" that "before I can use a GPIO, I have to > explicitly set its direction, even if the current reported direction is > what I want". A number of our customers have tried to use a GPIO which > states its an 'input' as an input after exporting it, which is > completely logical. But it doesn't work, because its not really an > input... Why not set the direction accurately as 'unknown' so users > intuitively know they have to set the direction before using it? You > also mention that it would be a nice feature above, so why not include > it?
I don't like what it does to the implementation, and I'd rather make drivers provide accurate data at the outset.
g.
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