How do can I find out which Linux driver is hogging my GPIO?

Question

I have a pad multiplxed as GPIO on my board. When I try to export it via /sys/class/gpio/export, I get

-sh: echo: write error: Device or resource busy 

My guess is some other driver is requesting this pad before I get that chance. How can I find out what is reserving it?

Answer 1

On the Boundary Devices kernel, and maybe others, you can use cat /sys/kernel/debug/gpio to get a list of the mapped gpios, their states, and name given when it was allocated. You can grep the kernel source for the name and find out what module grabbed it.

root@nitrogen6x:/opt# cat /sys/kernel/debug/gpio  GPIOs 0-31, platform/209c000.gpio, 209c000.gpio:  gpio-2   (flexcan-trx-stby    ) out lo      gpio-17  (DISP_SCL            ) out lo      GPIOs 32-63, platform/20a0000.gpio, 20a0000.gpio:  gpio-33  (sysfs               ) out lo      gpio-35  (sysfs               ) in  hi      gpio-36  (sysfs               ) in  hi      gpio-37  (DISP_SDI            ) out lo      gpio-38  (219c000.usdhc cd    ) in  hi      GPIOs 64-95, platform/20a4000.gpio, 20a4000.gpio:  gpio-83  (spi_imx             ) out lo      gpio-86  (usb_otg_vbus        ) out lo      GPIOs 96-127, platform/20a8000.gpio, 20a8000.gpio:  gpio-101 (sysfs               ) in  hi      gpio-116 (rst-gpios           ) out lo      GPIOs 128-159, platform/20ac000.gpio, 20ac000.gpio:  GPIOs 160-191, platform/20b0000.gpio, 20b0000.gpio:  gpio-175 (wlan-en             ) out lo      gpio-176 (bt_rfkill_reset     ) out lo      GPIOs 192-223, platform/20b4000.gpio, 20b4000.gpio:  gpio-192 (2198000.usdhc cd    ) in  lo      gpio-204 (ehci_reset_gpio     ) out lo      gpio-205 (sysfs               ) in  lo     

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Answer 2

if you try to use cat /sys/kernel/debug/gpio and it is not working, first try:

mount -t debugfs debugfs /sys/kernel/debug 

and then use the aforementioned cat command