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>

1 files changed, 122 insertions, 1 deletions

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index a2f1cd3766f3..eb084fa0df83 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -38,11 +38,12 @@
 #include "i2c-core.h"
 
 
-/* core_lock protects i2c_adapter_idr, and guarantees
+/* core_lock protects i2c_adapter_idr, userspace_devices, and guarantees
    that device detection, deletion of detected devices, and attach_adapter
    and detach_adapter calls are serialized */
 static DEFINE_MUTEX(core_lock);
 static DEFINE_IDR(i2c_adapter_idr);
+static LIST_HEAD(userspace_devices);
 
 static int i2c_check_addr(struct i2c_adapter *adapter, int addr);
 static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);
@@ -373,8 +374,128 @@ show_adapter_name(struct device *dev, struct device_attribute *attr, char *buf)
         return sprintf(buf, "%s\n", adap->name);
 }
 
+/*
+ * Let users instantiate I2C devices through sysfs. This can be used when
+ * platform initialization code doesn't contain the proper data for
+ * whatever reason. Also useful for drivers that do device detection and
+ * detection fails, either because the device uses an unexpected address,
+ * or this is a compatible device with different ID register values.
+ *
+ * Parameter checking may look overzealous, but we really don't want
+ * the user to provide incorrect parameters.
+ */
+static ssize_t
+i2c_sysfs_new_device(struct device *dev, struct device_attribute *attr,
+                     const char *buf, size_t count)
+{
+        struct i2c_adapter *adap = to_i2c_adapter(dev);
+        struct i2c_board_info info;
+        struct i2c_client *client;
+        char *blank, end;
+        int res;
+
+        dev_warn(dev, "The new_device interface is still experimental "
+                 "and may change in a near future\n");
+        memset(&info, 0, sizeof(struct i2c_board_info));
+
+        blank = strchr(buf, ' ');
+        if (!blank) {
+                dev_err(dev, "%s: Missing parameters\n", "new_device");
+                return -EINVAL;
+        }
+        if (blank - buf > I2C_NAME_SIZE - 1) {
+                dev_err(dev, "%s: Invalid device name\n", "new_device");
+                return -EINVAL;
+        }
+        memcpy(info.type, buf, blank - buf);
+
+        /* Parse remaining parameters, reject extra parameters */
+        res = sscanf(++blank, "%hi%c", &info.addr, &end);
+        if (res < 1) {
+                dev_err(dev, "%s: Can't parse I2C address\n", "new_device");
+                return -EINVAL;
+        }
+        if (res > 1  && end != '\n') {
+                dev_err(dev, "%s: Extra parameters\n", "new_device");
+                return -EINVAL;
+        }
+
+        if (info.addr < 0x03 || info.addr > 0x77) {
+                dev_err(dev, "%s: Invalid I2C address 0x%hx\n", "new_device",
+                        info.addr);
+                return -EINVAL;
+        }
+
+        client = i2c_new_device(adap, &info);
+        if (!client)
+                return -EEXIST;
+
+        /* Keep track of the added device */
+        mutex_lock(&core_lock);
+        list_add_tail(&client->detected, &userspace_devices);
+        mutex_unlock(&core_lock);
+        dev_info(dev, "%s: Instantiated device %s at 0x%02hx\n", "new_device",
+                 info.type, info.addr);
+
+        return count;
+}
+
+/*
+ * And of course let the users delete the devices they instantiated, if
+ * they got it wrong. This interface can only be used to delete devices
+ * instantiated by i2c_sysfs_new_device above. This guarantees that we
+ * don't delete devices to which some kernel code still has references.
+ *
+ * Parameter checking may look overzealous, but we really don't want
+ * the user to delete the wrong device.
+ */
+static ssize_t
+i2c_sysfs_delete_device(struct device *dev, struct device_attribute *attr,
+                        const char *buf, size_t count)
+{
+        struct i2c_adapter *adap = to_i2c_adapter(dev);
+        struct i2c_client *client, *next;
+        unsigned short addr;
+        char end;
+        int res;
+
+        /* Parse parameters, reject extra parameters */
+        res = sscanf(buf, "%hi%c", &addr, &end);
+        if (res < 1) {
+                dev_err(dev, "%s: Can't parse I2C address\n", "delete_device");
+                return -EINVAL;
+        }
+        if (res > 1  && end != '\n') {
+                dev_err(dev, "%s: Extra parameters\n", "delete_device");
+                return -EINVAL;
+        }
+
+        /* Make sure the device was added through sysfs */
+        res = -ENOENT;
+        mutex_lock(&core_lock);
+        list_for_each_entry_safe(client, next, &userspace_devices, detected) {
+                if (client->addr == addr && client->adapter == adap) {
+                        dev_info(dev, "%s: Deleting device %s at 0x%02hx\n",
+                                 "delete_device", client->name, client->addr);
+
+                        list_del(&client->detected);
+                        i2c_unregister_device(client);
+                        res = count;
+                        break;
+                }
+        }
+        mutex_unlock(&core_lock);
+
+        if (res < 0)
+                dev_err(dev, "%s: Can't find device in list\n",
+                        "delete_device");
+        return res;
+}
+
 static struct device_attribute i2c_adapter_attrs[] = {
         __ATTR(name, S_IRUGO, show_adapter_name, NULL),
+        __ATTR(new_device, S_IWUSR, NULL, i2c_sysfs_new_device),
+        __ATTR(delete_device, S_IWUSR, NULL, i2c_sysfs_delete_device),
         { },
 };