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gpio: pcf857x: implement get_direction()

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The GPIO core warns (and taints the kernel) when a gpiochip lacks
.get_direction() and a consumer queries a line's direction, for example
via /sys/kernel/debug/gpio. pcf857x provided direction_input/output but
no get_direction.

These quasi-bidirectional expanders cannot report direction in hardware,
and the 'out' software latch alone is ambiguous - a released (input)
line and an output driven high both read back as a set bit. Track the
direction explicitly in a 'dir' latch updated by the direction_input(),
direction_output() and set_multiple() paths, and return it from
get_direction(). Initialise it from the same reset state as 'out':
released lines are inputs, lines flagged in the power-on latch are
driven-low outputs.

Fixes: 15fae37d9f ("gpiolib: pcf857x i2c gpio expander support")
Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260825-b4-gpio-pcf857x-get-direction-v1-1-de15996ae354@vaisala.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
This commit is contained in:
Tapio Reijonen 2026-08-25 04:15:57 +00:00 committed by Bartosz Golaszewski
parent 78c0baf85c
commit ed14364ae8
1 changed files with 15 additions and 1 deletions
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16
drivers/gpio/gpio-pcf857x.c
View File

@ -71,8 +71,9 @@ MODULE_DEVICE_TABLE(of, pcf857x_of_table);
struct pcf857x {
struct gpio_chip chip;
struct i2c_client *client;
struct mutex lock; /* protect 'out' */
struct mutex lock; /* protect 'out' and 'dir' */
unsigned int out; /* software latch */
unsigned int dir; /* direction latch (1 = input) */
unsigned int status; /* current status */
unsigned int irq_enabled; /* enabled irqs */
@ -126,12 +127,21 @@ static int pcf857x_input(struct gpio_chip *chip, unsigned int offset)
mutex_lock(&gpio->lock);
gpio->out |= (1 << offset);
gpio->dir |= (1 << offset);
status = gpio->write(gpio->client, gpio->out);
mutex_unlock(&gpio->lock);
return status;
}
static int pcf857x_get_direction(struct gpio_chip *chip, unsigned int offset)
{
struct pcf857x *gpio = gpiochip_get_data(chip);
return (gpio->dir & (1 << offset)) ? GPIO_LINE_DIRECTION_IN
: GPIO_LINE_DIRECTION_OUT;
}
static int pcf857x_get(struct gpio_chip *chip, unsigned int offset)
{
struct pcf857x *gpio = gpiochip_get_data(chip);
@ -167,6 +177,7 @@ static int pcf857x_output(struct gpio_chip *chip, unsigned int offset, int value
gpio->out |= bit;
else
gpio->out &= ~bit;
gpio->dir &= ~bit;
status = gpio->write(gpio->client, gpio->out);
mutex_unlock(&gpio->lock);
@ -187,6 +198,7 @@ static int pcf857x_set_multiple(struct gpio_chip *chip, unsigned long *mask,
mutex_lock(&gpio->lock);
gpio->out &= ~*mask;
gpio->out |= *bits & *mask;
gpio->dir &= ~*mask;
status = gpio->write(gpio->client, gpio->out);
mutex_unlock(&gpio->lock);
@ -301,6 +313,7 @@ static int pcf857x_probe(struct i2c_client *client)
gpio->chip.set_multiple = pcf857x_set_multiple;
gpio->chip.direction_input = pcf857x_input;
gpio->chip.direction_output = pcf857x_output;
gpio->chip.get_direction = pcf857x_get_direction;
gpio->chip.ngpio = (uintptr_t)i2c_get_match_data(client);
reset_gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
@ -396,6 +409,7 @@ static int pcf857x_probe(struct i2c_client *client)
* reset state. Otherwise it flags pins to be driven low.
*/
gpio->out = ~n_latch;
gpio->dir = ~n_latch;
gpio->status = gpio->read(gpio->client);
/* Enable irqchip if we have an interrupt */