Letux Kernel

Issue 658: tca6424: allow to configure outputs as "virtual open-drain"

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 


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


Labels: Type:Enhancement Type:Defect
Status: Ready

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 

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.
Status: Fixed
Owner: hns

Comment 3 by Nikolaus Schaller, Nov 4, 2014

"Fixed" status means "closed"...
Labels: Device:Pyra
Status: Ready

Comment 4 by Nikolaus Schaller, Oct 26, 2015

Since we connect the LEDs to a different controller, we do no longer 
need this feature.
Status: WontFix

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Created: 9 years 10 months ago by Nikolaus Schaller

Updated: 4 years 7 months ago

Status: WontFix

Owner: Nikolaus Schaller

Followed by: 2 persons