Reported by Nikolaus Schaller, Sep 8, 2014
on the pyra board we connect some LEDs between the outputs and VSYS. Since the outputs are totem-pole between 1.8V and 0V, even an active high output sends enough current through the LEDs so that they glow visible. Solution: extend drivers/gpio/gpio-pca953x.c so that each gpio pin can be configured to be a virtual open drain or totem pole. This can be achieved by making the pin an input if a "1" is written and only an output if a "0" is written. To configure we needs another byte-array for this setting anda device tree node to configure it. E.g.: open-drain-pins = <1 4 6 9>;
Comment 1 by Nikolaus Schaller, Sep 30, 2014
done: http://git.goldelico.com/?p=gta04-kernel.git;a=commit;h=16e799bd6af8c 6b71f8e90b9c606309b362651d8
Comment 2 by Nikolaus Schaller, Nov 4, 2014
I have learned from studying the data sheet is that in input mode every change of an input triggers an interrupt. Which can't be masked on tca6424 level but must be masked by the driver after reading the input registers through I2C. This is very time consuming. What is not described in the data sheet is how the chip behaves when switching from output to input and vice versa. If (and under which conditions) this triggers a spurious interrupt wasting CPU time. Therefore this topic is rolled back to status "fixed" because it works, but needs more QA before upstreaming.
Comment 3 by Nikolaus Schaller, Nov 4, 2014
"Fixed" status means "closed"...
Comment 4 by Nikolaus Schaller, Oct 26, 2015
Since we connect the LEDs to a different controller, we do no longer need this feature.
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