Messages in this thread | | | Date | Tue, 19 Nov 2013 10:59:39 -0800 | Subject | Re: [PATCH] pinctrl: samsung: Allow pin value to be initialized using pinfunc. | From | Doug Anderson <> |
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On Tue, Nov 19, 2013 at 10:46 AM, Stephen Warren <swarren@wwwdotorg.org> wrote: > On 11/19/2013 10:15 AM, Tomasz Figa wrote: >> This patch extends the range of settings configurable via pinfunc API >> to cover pin value as well. This allows configuration of default values >> of pins. > > Shouldn't there be a driver that acquires the GPIO that's output to the > pin, and configures the output value? IIRC there have been previous > discussions re: having a list of e.g. initial GPIO output values in DT, > and that was rejected, and this patch seems to be doing almost the exact > same thing, just at the pinctrl level rather than GPIO level. > > That all said, I admit this could be a useful feature...
I haven't followed all of the previous discussions, but I know I've run into scenarios where something like this would be useful. The one that comes to mind is:
* We've got GPIOs that default at bootup to a pulled up input since the default state of the pin should be "high".
* These pins are really intended to be outputs, like an "enable", "reset", or "power down" line for a peripheral. The pullup is strong enough to give us a good default state but we really want outputs.
* We'd like to provide this GPIO to a peripheral through device tree. ...and we'd like all the pinmux to be setup automatically so we use pinctrl-names = "default".
* If we set the pinmux up as "output" then there's a chance that the line will glitch at bootup since the pinmux happens (changing the pin to output) before the driver has a chance to run.
Does that sound like the same scenario you're trying to solve Tomasz?
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