On Wed, Feb 10, 2021 at 9:50 AM Drew Fustini [off-list ref] wrote:

Add "pinmux-select" to debugfs which will activate a function and group
when 2 integers "<function-selector> <group-selector>" are written to
the file. The write operation pinmux_select() handles this by checking
if fsel and gsel are valid selectors and then calling ops->set_mux().

The existing "pinmux-functions" debugfs file lists the pin functions
registered for the pin controller. For example:

function: pinmux-uart0, groups = [ pinmux-uart0-pins ]
function: pinmux-mmc0, groups = [ pinmux-mmc0-pins ]
function: pinmux-mmc1, groups = [ pinmux-mmc1-pins ]
function: pinmux-i2c0, groups = [ pinmux-i2c0-pins ]
function: pinmux-i2c1, groups = [ pinmux-i2c1-pins ]
function: pinmux-spi1, groups = [ pinmux-spi1-pins ]

To activate function pinmux-i2c1 (fsel 4) and group pinmux-i2c1-pins
(gsel 4):

echo '4 4' > pinmux-select

...

 DEFINE_SHOW_ATTRIBUTE(pinmux_pins);

+

One blank line (existed) is enough.

+#define PINMUX_MAX_NAME 64

...

+       buf = devm_kzalloc(pctldev->dev, PINMUX_MAX_NAME * 2, GFP_KERNEL);

You have to (re-)read documentation about Device Managed Resources.
Keyword here is *device*! Pay attention to it. TL;DR: misuse of device
managed resources here.
Potentially memory exhausting (local DoS attack), but see below.

+       if (!buf)
+               return -ENOMEM;

...

+       devm_kfree(pctldev->dev, buf);

Calling devm_kfree() or other devm_*() release kinda APIs is a red
flag in 99%. See above.

--
With Best Regards,
Andy Shevchenko