[PATCH v3] gpio: exar: set value when external pull-up or pull-down is present

[Sai Kumar Cholleti <skmr537@xxxxxxxxx>]

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@xxxxxxxxxxx>
Signed-off-by: Matthew McClain <mmcclain@xxxxxxxxxxx>
Signed-off-by: Sai Kumar Cholleti <skmr537@xxxxxxxxx>
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..d5909a4f0433 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