[RFC PATCH 4/5] gpio: gpiolib: Add sysfs support for maintaining GPIO values on reset

Andrew Jeffery
2017-10-20T03:37:26Z

Expose a new 'maintain' sysfs attribute to control both suspend and
reset tolerance.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
---
Documentation/gpio/sysfs.txt | 9 +++++
drivers/gpio/gpiolib-sysfs.c | 88 ++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 93 insertions(+), 4 deletions(-)

diff --git a/Documentation/gpio/sysfs.txt b/Documentation/gpio/sysfs.txt
index aeab01aa4d00..f447f0746884 100644
--- a/Documentation/gpio/sysfs.txt
+++ b/Documentation/gpio/sysfs.txt
@@ -96,6 +96,15 @@ and have the following read/write attributes:
for "rising" and "falling" edges will follow this
setting.

+ "maintain" ... displays and controls whether the state of the GPIO is
+ maintained or lost on suspend or reset. The valid values take
+ the following meanings:
+
+ 0: Do not maintain state on either suspend or reset
+ 1: Maintain state for suspend only
+ 2: Maintain state for reset only
+ 3: Maintain state for both suspend and reset
+
GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the
controller implementing GPIOs starting at #42) and have the following
read-only attributes:
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 3f454eaf2101..bfa186e73e26 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -289,6 +289,74 @@ static ssize_t edge_store(struct device *dev,
}
static DEVICE_ATTR_RW(edge);

+#define GPIOLIB_SYSFS_MAINTAIN_SUSPEND BIT(0)
+#define GPIOLIB_SYSFS_MAINTAIN_RESET BIT(1)
+#define GPIOLIB_SYSFS_MAINTAIN_ALL GENMASK(1, 0)
+static ssize_t maintain_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct gpiod_data *data = dev_get_drvdata(dev);
+ ssize_t status = 0;
+ int val = 0;
+
+ mutex_lock(&data->mutex);
+
+ if (!test_bit(FLAG_SLEEP_MAY_LOSE_VALUE, &data->desc->flags))
+ val |= GPIOLIB_SYSFS_MAINTAIN_SUSPEND;
+
+ if (test_bit(FLAG_RESET_TOLERANT, &data->desc->flags))
+ val |= GPIOLIB_SYSFS_MAINTAIN_RESET;
+
+ status = sprintf(buf, "%d\n", val);
+
+ mutex_unlock(&data->mutex);
+
+ return status;
+}
+
+static ssize_t maintain_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t size)
+{
+ struct gpiod_data *data = dev_get_drvdata(dev);
+ struct gpio_chip *chip;
+ ssize_t status;
+ long provided;
+
+ mutex_lock(&data->mutex);
+
+ chip = data->desc->gdev->chip;
+
+ if (!chip->set_config)
+ return -ENOTSUPP;
+
+ status = kstrtol(buf, 0, &provided);
+ if (status < 0)
+ goto out;
+
+ if (provided & ~GPIOLIB_SYSFS_MAINTAIN_ALL) {
+ status = -EINVAL;
+ goto out;
+ }
+
+ if (!(provided & GPIOLIB_SYSFS_MAINTAIN_SUSPEND))
+ set_bit(FLAG_SLEEP_MAY_LOSE_VALUE, &data->desc->flags);
+ else
+ clear_bit(FLAG_SLEEP_MAY_LOSE_VALUE,
+ &data->desc->flags);
+
+ /* Configure reset tolerance */
+ status = gpiod_set_reset_tolerant(data->desc,
+ !!(provided & GPIOLIB_SYSFS_MAINTAIN_RESET));
+out:
+ mutex_unlock(&data->mutex);
+
+ return status ? : size;
+
+}
+static DEVICE_ATTR_RW(maintain);
+
/* Caller holds gpiod-data mutex. */
static int gpio_sysfs_set_active_low(struct device *dev, int value)
{
@@ -378,6 +446,7 @@ static struct attribute *gpio_attrs[] = {
&dev_attr_edge.attr,
&dev_attr_value.attr,
&dev_attr_active_low.attr,
+ &dev_attr_maintain.attr,
NULL,
};

@@ -474,11 +543,22 @@ static ssize_t export_store(struct class *class,
status = -ENODEV;
goto done;
}
- status = gpiod_export(desc, true);
- if (status < 0)
+
+ /*
+ * If userspace is requesting the GPIO via sysfs, make them explicitly
+ * configure reset tolerance each time by unconditionally disabling it
+ * here, as the export and configuration steps are not atomic.
+ */
+ status = gpiod_set_reset_tolerant(desc, false);
+ if (status < 0) {
gpiod_free(desc);
- else
- set_bit(FLAG_SYSFS, &desc->flags);
+ } else {
+ status = gpiod_export(desc, true);
+ if (status < 0)
+ gpiod_free(desc);
+ else
+ set_bit(FLAG_SYSFS, &desc->flags);
+ }

done:
if (status)
--
2.11.0