i2c: Add a sysfs interface to instantiate devices
Add a sysfs interface to instantiate and delete I2C devices. This is primarily a replacement of the force_* module parameters implemented by some i2c drivers. These module parameters were implemented internally by the I2C_CLIENT_INSMOD* macros, which don't scale well. This can also be used when developing a driver on a self-soldered board which doesn't yet have proper I2C device declaration at the platform level, and presumably for various debugging situations. Signed-off-by: Jean Delvare <khali@linux-fr.org> Cc: David Brownell <dbrownell@users.sourceforge.net>
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Jean Delvare
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35fc37f818
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99cd8e2587
3 changed files with 168 additions and 2 deletions
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@ -165,3 +165,47 @@ was done there. Two significant differences are:
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Once again, method 3 should be avoided wherever possible. Explicit device
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instantiation (methods 1 and 2) is much preferred for it is safer and
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faster.
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Method 4: Instantiate from user-space
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-------------------------------------
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In general, the kernel should know which I2C devices are connected and
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what addresses they live at. However, in certain cases, it does not, so a
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sysfs interface was added to let the user provide the information. This
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interface is made of 2 attribute files which are created in every I2C bus
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directory: new_device and delete_device. Both files are write only and you
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must write the right parameters to them in order to properly instantiate,
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respectively delete, an I2C device.
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File new_device takes 2 parameters: the name of the I2C device (a string)
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and the address of the I2C device (a number, typically expressed in
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hexadecimal starting with 0x, but can also be expressed in decimal.)
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File delete_device takes a single parameter: the address of the I2C
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device. As no two devices can live at the same address on a given I2C
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segment, the address is sufficient to uniquely identify the device to be
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deleted.
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Example:
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# echo eeprom 0x50 > /sys/class/i2c-adapter/i2c-3/new_device
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While this interface should only be used when in-kernel device declaration
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can't be done, there is a variety of cases where it can be helpful:
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* The I2C driver usually detects devices (method 3 above) but the bus
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segment your device lives on doesn't have the proper class bit set and
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thus detection doesn't trigger.
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* The I2C driver usually detects devices, but your device lives at an
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unexpected address.
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* The I2C driver usually detects devices, but your device is not detected,
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either because the detection routine is too strict, or because your
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device is not officially supported yet but you know it is compatible.
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* You are developing a driver on a test board, where you soldered the I2C
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device yourself.
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This interface is a replacement for the force_* module parameters some I2C
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drivers implement. Being implemented in i2c-core rather than in each
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device driver individually, it is much more efficient, and also has the
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advantage that you do not have to reload the driver to change a setting.
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You can also instantiate the device before the driver is loaded or even
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available, and you don't need to know what driver the device needs.
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@ -38,11 +38,12 @@
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#include "i2c-core.h"
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/* core_lock protects i2c_adapter_idr, and guarantees
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/* core_lock protects i2c_adapter_idr, userspace_devices, and guarantees
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that device detection, deletion of detected devices, and attach_adapter
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and detach_adapter calls are serialized */
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static DEFINE_MUTEX(core_lock);
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static DEFINE_IDR(i2c_adapter_idr);
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static LIST_HEAD(userspace_devices);
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static int i2c_check_addr(struct i2c_adapter *adapter, int addr);
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static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);
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@ -373,8 +374,128 @@ show_adapter_name(struct device *dev, struct device_attribute *attr, char *buf)
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return sprintf(buf, "%s\n", adap->name);
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}
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/*
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* Let users instantiate I2C devices through sysfs. This can be used when
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* platform initialization code doesn't contain the proper data for
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* whatever reason. Also useful for drivers that do device detection and
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* detection fails, either because the device uses an unexpected address,
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* or this is a compatible device with different ID register values.
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*
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* Parameter checking may look overzealous, but we really don't want
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* the user to provide incorrect parameters.
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*/
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static ssize_t
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i2c_sysfs_new_device(struct device *dev, struct device_attribute *attr,
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const char *buf, size_t count)
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{
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struct i2c_adapter *adap = to_i2c_adapter(dev);
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struct i2c_board_info info;
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struct i2c_client *client;
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char *blank, end;
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int res;
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dev_warn(dev, "The new_device interface is still experimental "
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"and may change in a near future\n");
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memset(&info, 0, sizeof(struct i2c_board_info));
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blank = strchr(buf, ' ');
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if (!blank) {
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dev_err(dev, "%s: Missing parameters\n", "new_device");
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return -EINVAL;
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}
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if (blank - buf > I2C_NAME_SIZE - 1) {
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dev_err(dev, "%s: Invalid device name\n", "new_device");
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return -EINVAL;
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}
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memcpy(info.type, buf, blank - buf);
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/* Parse remaining parameters, reject extra parameters */
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res = sscanf(++blank, "%hi%c", &info.addr, &end);
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if (res < 1) {
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dev_err(dev, "%s: Can't parse I2C address\n", "new_device");
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return -EINVAL;
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}
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if (res > 1 && end != '\n') {
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dev_err(dev, "%s: Extra parameters\n", "new_device");
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return -EINVAL;
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}
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if (info.addr < 0x03 || info.addr > 0x77) {
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dev_err(dev, "%s: Invalid I2C address 0x%hx\n", "new_device",
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info.addr);
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return -EINVAL;
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}
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client = i2c_new_device(adap, &info);
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if (!client)
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return -EEXIST;
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/* Keep track of the added device */
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mutex_lock(&core_lock);
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list_add_tail(&client->detected, &userspace_devices);
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mutex_unlock(&core_lock);
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dev_info(dev, "%s: Instantiated device %s at 0x%02hx\n", "new_device",
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info.type, info.addr);
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return count;
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}
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/*
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* And of course let the users delete the devices they instantiated, if
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* they got it wrong. This interface can only be used to delete devices
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* instantiated by i2c_sysfs_new_device above. This guarantees that we
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* don't delete devices to which some kernel code still has references.
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*
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* Parameter checking may look overzealous, but we really don't want
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* the user to delete the wrong device.
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*/
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static ssize_t
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i2c_sysfs_delete_device(struct device *dev, struct device_attribute *attr,
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const char *buf, size_t count)
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{
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struct i2c_adapter *adap = to_i2c_adapter(dev);
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struct i2c_client *client, *next;
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unsigned short addr;
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char end;
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int res;
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/* Parse parameters, reject extra parameters */
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res = sscanf(buf, "%hi%c", &addr, &end);
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if (res < 1) {
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dev_err(dev, "%s: Can't parse I2C address\n", "delete_device");
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return -EINVAL;
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}
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if (res > 1 && end != '\n') {
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dev_err(dev, "%s: Extra parameters\n", "delete_device");
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return -EINVAL;
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}
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/* Make sure the device was added through sysfs */
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res = -ENOENT;
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mutex_lock(&core_lock);
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list_for_each_entry_safe(client, next, &userspace_devices, detected) {
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if (client->addr == addr && client->adapter == adap) {
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dev_info(dev, "%s: Deleting device %s at 0x%02hx\n",
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"delete_device", client->name, client->addr);
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list_del(&client->detected);
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i2c_unregister_device(client);
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res = count;
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break;
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}
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}
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mutex_unlock(&core_lock);
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if (res < 0)
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dev_err(dev, "%s: Can't find device in list\n",
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"delete_device");
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return res;
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}
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static struct device_attribute i2c_adapter_attrs[] = {
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__ATTR(name, S_IRUGO, show_adapter_name, NULL),
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__ATTR(new_device, S_IWUSR, NULL, i2c_sysfs_new_device),
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__ATTR(delete_device, S_IWUSR, NULL, i2c_sysfs_delete_device),
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{ },
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};
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@ -178,7 +178,8 @@ struct i2c_driver {
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* @driver: device's driver, hence pointer to access routines
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* @dev: Driver model device node for the slave.
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* @irq: indicates the IRQ generated by this device (if any)
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* @detected: member of an i2c_driver.clients list
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* @detected: member of an i2c_driver.clients list or i2c-core's
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* userspace_devices list
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*
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* An i2c_client identifies a single device (i.e. chip) connected to an
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* i2c bus. The behaviour exposed to Linux is defined by the driver
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