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Bug introduced in the of_get_named_gpiod_flags function.




Hi,

The function of_get_named_gpiod_flags in older versions of the kernel (up to 4.7.10 - https://elixir.bootlin.com/linux/v4.7.10/source/drivers/gpio/gpiolib-of.c#L75 )
contained an important workaround:

/* .of_xlate might decide to not fill in the flags, so clear it. */if (flags)
 *flags = 0;

Unfortunately, newer kernels do not contain it. Therefore if the
"xlat" function in the gpiochip driver does not set flags, (like e.g.
the Xilinx AXI GPIO driver: https://github.com/Xilinx/linux-xlnx/blob/c2ba891326bb472da59b6a2da29aca218d337687/drivers/gpio/gpio-xilinx.c#L262 )
the random, unitialized value from the stack in of_find_gpio ( https://elixir.bootlin.com/linux/v4.18.13/source/drivers/gpio/gpiolib-of.c#L228 )
is used, which results in random settings of e.g., OPEN DRAIN or OPEN SOURCE mode.
I suppose, that either the workaround should be restored, ot the of_flags variable in of_find_gpio should be initialized.

I have also reported the problem in the Xilinx forum: https://forums.xilinx.com/t5/Embedded-Linux/Bug-in-of-get-named-gpiod-flags-function-in-the-kernel-random/td-p/897695

With best regards,
Wojciech Zabolotny