[PATCH] gpio: exar set value handling for hw with gpio pull-up or pull-down

[Sai Kumar Cholleti <skmr537@gmail.com>]

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 input to output,
exar_set_value is set to 1, but since direction is input when
exar_set_value is called, _regmap_update_bits reads a 1 due to an
external pull-up.  When force_write is not set (regmap_set_bits has
force_write = false), the value 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

Signed-off-by: Sai Kumar Cholleti <skmr537@gmail.com>
---
 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 482f678c893e..de5ce73159cb 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