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Old 05-27-2015, 03:44 PM   #1
newhorizon101
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Registered: Apr 2014
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Linux GPIO Driver


Hi All,

I am trying to play with the gpio subsystem. I have a question, is there a way to hardcode the gpio number with regards to /sys/class/gpiochipxxx

I have multiple platforms and I would like to have same code run on both platforms, if some how I can tell driver to tell gpio subsystem of a fixed gpio number.

Thanks,
 
Old 05-29-2015, 09:58 PM   #2
ferrari
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My understanding is that the device number xxx represents the base address so this should already be persistent? My apologies in advance if I don't quite understand your question, but the answer will almost certainly involve udev

For example, if I do
Code:
udevadm info -a -p /devices/virtual/gpio/gpiochip240
I get
Code:
Udevadm info starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

  looking at device '/devices/virtual/gpio/gpiochip240':
    KERNEL=="gpiochip240"
    SUBSYSTEM=="gpio"
    DRIVER==""
    ATTR{base}=="240"
    ATTR{label}=="ssb_chipco_gpio"
    ATTR{ngpio}=="16"
In general it is possible to create a udev rule to recognise a specific device in question (using unique device attributes) and assign a desired preferred name (via symlink).
 
Old 05-29-2015, 10:40 PM   #3
ferrari
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The following reference might also be useful

http://www.wiki.xilinx.com/Linux+GPIO+Driver

They have an example user-space application that might help with your code too.

This GPIO User space app mentions
Code:
// Figuring out the exact GPIO was not totally obvious when there
// were multiple GPIOs in the system. One way to do is to go into
// the gpiochips in /sys/class/gpio and view the label as it should
// reflect the address of the GPIO in the system. The name of the
// the chip appears to be the 1st GPIO of the controller.
 
  


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