Kernel/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2025-01-17 02:36:21 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

gpio: exar: set value when external pull-up or pull-down is present

Browse Source 
Setting GPIO direction = high, sometimes results in GPIO value = 0.

If a GPIO is pulled high, the following construction results in the
value being 0 when the desired value is 1:

$ echo "high" > /sys/class/gpio/gpio336/direction
$ cat /sys/class/gpio/gpio336/value
0

Before the GPIO direction is changed from an input to an output,
exar_set_value() is called with value = 1, but since the GPIO is an
input when exar_set_value() is called, _regmap_update_bits() reads a 1
due to an external pull-up.  regmap_set_bits() sets force_write =
false, so the value (1) is not written.  When the direction is then
changed, the GPIO becomes an output with the value of 0 (the hardware
default).

regmap_write_bits() sets force_write = true, so the value is always
written by exar_set_value() and an external pull-up doesn't affect the
outcome of setting direction = high.

The same can happen when a GPIO is pulled low, but the scenario is a
little more complicated.

$ echo high > /sys/class/gpio/gpio351/direction
$ cat /sys/class/gpio/gpio351/value
1

$ echo in > /sys/class/gpio/gpio351/direction
$ cat /sys/class/gpio/gpio351/value
0

$ echo low > /sys/class/gpio/gpio351/direction
$ cat /sys/class/gpio/gpio351/value
1

Fixes: 36fb7218e878 ("gpio: exar: switch to using regmap")
Co-developed-by: Matthew McClain <mmcclain@noprivs.com>
Signed-off-by: Matthew McClain <mmcclain@noprivs.com>
Signed-off-by: Sai Kumar Cholleti <skmr537@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20241105071523.2372032-1-skmr537@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
This commit is contained in:
Sai Kumar Cholleti 2024-11-05 12:45:23 +05:30 committed by Bartosz Golaszewski
parent c7899503ad
commit 72cef64180
1 changed files with 6 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
drivers/gpio/gpio-exar.c
View File

@ -99,11 +99,13 @@ static void exar_set_value(struct gpio_chip *chip, unsigned int offset,
struct exar_gpio_chip *exar_gpio = gpiochip_get_data(chip);
unsigned int addr = exar_offset_to_lvl_addr(exar_gpio, offset);
unsigned int bit = exar_offset_to_bit(exar_gpio, offset);
unsigned int bit_value = value ? BIT(bit) : 0;
if (value)
regmap_set_bits(exar_gpio->regmap, addr, BIT(bit));
else
regmap_clear_bits(exar_gpio->regmap, addr, BIT(bit));
/*
* regmap_write_bits() forces value to be written when an external
* pull up/down might otherwise indicate value was already set.
*/
regmap_write_bits(exar_gpio->regmap, addr, BIT(bit), bit_value);
}
static int exar_direction_output(struct gpio_chip *chip, unsigned int offset,