[PATH v3 3/4] i2c: show and change bus frequency via sysfs

Octavian Purdila
2014-10-15T20:03:59Z

This patch adds three new sysfs files: frequency, frequency_min and
frequency_max which allows the user to view or change the bus
frequency on a per bus level.

This is required for the case where multiple busses have the same
adapter driver in which case a module parameter does not allow
controlling the bus speed individually (e.g. USB I2C adapters).

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
---
Documentation/ABI/testing/sysfs-bus-i2c | 30 +++++++++++
drivers/i2c/i2c-core.c | 90 +++++++++++++++++++++++++++++++++
include/linux/i2c.h | 16 ++++++
3 files changed, 136 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-i2c b/Documentation/ABI/testing/sysfs-bus-i2c
index 8075585..70af81f 100644
--- a/Documentation/ABI/testing/sysfs-bus-i2c
+++ b/Documentation/ABI/testing/sysfs-bus-i2c
@@ -43,3 +43,33 @@ Contact: linux-i2c@vger.kernel.org
Description:
An i2c device attached to bus X that is enumerated via
ACPI. Y is the ACPI device name and its format is "%s".
+
+What: /sys/bus/i2c/devices/i2c-X/frequency
+KernelVersion: 3.19
+Contact: linux-i2c@vger.kernel.org
+Description:
+ The current bus frequency for bus X. Can be updated if
+ the bus supports it. The unit is HZ and format is
+ "%d\n".
+ If the bus does not support changing the frequency
+ then this entry will be read-only.
+ If the bus does not support showing the frequency than
+ this entry will not be visible.
+ When updating the bus frequency that value must be in
+ the range defined by bus_frequency_min and
+ bus_frequency_max otherwise writing to this entry will
+ fail with -EINVAL.
+ The bus may not support all of the frequencies in the
+ min-max range and may round the frequency to the
+ closest supported one. The user must read the entry
+ after writing it to retrieve the actual set frequency.
+
+What: /sys/bus/i2c/devices/i2c-X/frequency_min
+What: /sys/bus/i2c/devices/i2c-X/frequency_max
+KernelVersion: 3.19
+Contact: linux-i2c@vger.kernel.org
+Description:
+ Minimum and maximum frequencies for bus X. The unit is
+ HZ and format is "%d\n".
+ If the bus does not support changing the frequency
+ these entries will not be visible.
diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 632057a..27c29eb 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -940,15 +940,97 @@ static DEVICE_ATTR(new_device, S_IWUSR, NULL, i2c_sysfs_new_device);
static DEVICE_ATTR_IGNORE_LOCKDEP(delete_device, S_IWUSR, NULL,
i2c_sysfs_delete_device);

+static ssize_t
+i2c_sysfs_freq_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct i2c_adapter *adap = to_i2c_adapter(dev);
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", adap->freq);
+}
+
+static ssize_t
+i2c_sysfs_freq_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct i2c_adapter *adap = to_i2c_adapter(dev);
+ unsigned int freq;
+ int ret;
+
+ if (kstrtouint(buf, 0, &freq) || freq < adap->min_freq ||
+ freq > adap->max_freq)
+ return -EINVAL;
+
+ i2c_lock_adapter(adap);
+ ret = adap->set_freq(adap, &freq);
+ i2c_unlock_adapter(adap);
+
+ if (ret)
+ return ret;
+
+ adap->freq = freq;
+
+ return count;
+}
+
+static DEVICE_ATTR(frequency, S_IRUGO, i2c_sysfs_freq_show,
+ i2c_sysfs_freq_store);
+
+static ssize_t frequency_min_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct i2c_adapter *adap = to_i2c_adapter(dev);
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", adap->min_freq);
+}
+
+static DEVICE_ATTR_RO(frequency_min);
+
+static ssize_t frequency_max_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct i2c_adapter *adap = to_i2c_adapter(dev);
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", adap->max_freq);
+}
+
+static DEVICE_ATTR_RO(frequency_max);
+
+static umode_t i2c_adapter_visible_attr(struct kobject *kobj,
+ struct attribute *attr, int idx)
+{
+ struct device *dev = container_of(kobj, struct device, kobj);
+ struct i2c_adapter *adap = to_i2c_adapter(dev);
+ umode_t mode = attr->mode;
+
+ if (attr == &dev_attr_frequency_min.attr)
+ return adap->min_freq ? mode : 0;
+
+ if (attr == &dev_attr_frequency_max.attr)
+ return adap->max_freq ? mode : 0;
+
+ if (attr == &dev_attr_frequency.attr) {
+ if (adap->set_freq)
+ mode |= S_IWUSR;
+ return adap->freq ? mode : 0;
+ }
+
+ return mode;
+}
+
static struct attribute *i2c_adapter_attrs[] = {
&dev_attr_name.attr,
&dev_attr_new_device.attr,
&dev_attr_delete_device.attr,
+ &dev_attr_frequency.attr,
+ &dev_attr_frequency_min.attr,
+ &dev_attr_frequency_max.attr,
NULL
};

static struct attribute_group i2c_adapter_attr_group = {
.attrs = i2c_adapter_attrs,
+ .is_visible = i2c_adapter_visible_attr,
};

static const struct attribute_group *i2c_adapter_attr_groups[] = {
@@ -1262,6 +1344,14 @@ int i2c_add_adapter(struct i2c_adapter *adapter)
struct device *dev = &adapter->dev;
int id;

+ if (adapter->set_freq) {
+ if (!adapter->freq || !adapter->min_freq || !adapter->max_freq)
+ return -EINVAL;
+ } else {
+ if (adapter->min_freq || adapter->max_freq)
+ return -EINVAL;
+ }
+
if (dev->of_node) {
id = of_alias_get_id(dev->of_node, "i2c");
if (id >= 0) {
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 36041e2..5d893f5 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -431,6 +431,17 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap);
* usb->interface->dev, platform_device->dev etc.)
* @name: name of this i2c bus
* @bus_recovery_info: see struct i2c_bus_recovery_info. Optional.
+ * @set_freq: set the bus frequency (in HZ) and returns the actual set
+ * value. Since not all the frequencies in the min - max interval
+ * may be valid the driver may round the frequency to the closest
+ * supported one. Optional but must be set if min_freq or
+ * max_freq is set.
+ * @min_freq: minimum bus frequency. Optional but must be set if
+ * set_freq is set.
+ * @max_freq: maximum bus frequency. Optional but must be set if
+ * set_freq is set.
+ * @freq: initial bus frequency. Optional but must be set if set_freq
+ * is set.
*/
struct i2c_adapter {
struct module *owner;
@@ -438,6 +449,11 @@ struct i2c_adapter {
const struct i2c_algorithm *algo; /* the algorithm to access the bus */
void *algo_data;

+ unsigned int freq;
+ unsigned int min_freq;
+ unsigned int max_freq;
+ int (*set_freq)(struct i2c_adapter *a, unsigned int *freq);
+
/* data fields that are valid for all devices */
struct rt_mutex bus_lock;

--
1.9.1