Suspicious debounce handling code in pintctrl-baytrail

[Jean Delvare <jdelvare@suse.de>]

Hi Cristina,

In this commit:

commit 658b476c742fe379e7020309fd590a27b457a4c1
Date:   Fri Apr 1 14:00:07 2016 +0300

    pinctrl: baytrail: Add debounce configuration

you added support for getting and setting debounce configuration for
the Baytrail pins. Now gcc complains about the following:

  CC [M]  drivers/pinctrl/intel/pinctrl-baytrail.o
drivers/pinctrl/intel/pinctrl-baytrail.c: In function ‘byt_pin_config_set’:
drivers/pinctrl/intel/pinctrl-baytrail.c:1181:17: warning: variable ‘debounce’ set but not used [-Wunused-but-set-variable]
  u32 conf, val, debounce;
                 ^

I looked at the code, and it indeed looks wrong. You are reading the
BYT_DEBOUNCE_REG register, clearing the debounce time bits from it, and
then writing the debounce time bits to the *BYT_CONF0_REG* register.
This is certainly corrupting the chip configuration, as the
configuration register bits 2-0 have a completely different meaning
(mux configuration.)

Did you ever test that code?

Additionally, I suspect that in the "get" path, the following is wrong:

	case PIN_CONFIG_INPUT_DEBOUNCE:
		if (!(conf & BYT_DEBOUNCE_EN))
			return -EINVAL;

I'm not familiar with the pinctrl interface but my understanding of
the PIN_CONFIG_INPUT_DEBOUNCE documentation is that the driver must
return 0 if debouncing is disabled. The "set" path would also need to
handle this case properly (setting BYT_DEBOUNCE_EN if debounce timing is
non-zero, clearing it if value is zero.)

-- 
Jean Delvare
SUSE L3 Support