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")
Signed-off-by: Sai Kumar Cholleti <skmr537@xxxxxxxxx>
Signed-off-by: Matthew McClain <mmcclain@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
drivers/gpio/gpio-exar.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/gpio/gpio-exar.c b/drivers/gpio/gpio-exar.c
index 5170fe7599cd..dfc7a9ca3e62 100644
--- a/drivers/gpio/gpio-exar.c
+++ b/drivers/gpio/gpio-exar.c
@@ -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,
--
2.34.1
