Extcon: support mutually exclusive relation between cables.

There could be cables that t recannot be attaches simulatenously. Extcon
device drivers may express such information via mutually_exclusive in
struct extcon_dev.

For example, for an extcon device with 16 cables (bits 0 to 15 are
available), if mutually_exclusive = { 0x7, 0xC0, 0x81, 0 }, then, the
following attachments are prohibitted.
{0, 1}
{0, 2}
{1, 2}
{6, 7}
{0, 7}
and every attachment set that are superset of one of the above.
For the detail, please refer to linux/include/linux/extcon.h.

The concept is suggested by NeilBrown <neilb@suse.de>

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

--
Changes from V5:
- Updated sysfs format
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 160 insertions, 13 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-extcon b/Documentation/ABI/testing/sysfs-class-extcon
index 19b18e986a57..20ab361bd8c6 100644
--- a/Documentation/ABI/testing/sysfs-class-extcon
+++ b/Documentation/ABI/testing/sysfs-class-extcon
@@ -15,6 +15,10 @@ Description:
                 may have both HDMI and Charger attached, or analog audio,
                 video, and USB cables attached simulteneously.
 
+                If there are cables mutually exclusive with each other,
+                such binary relations may be expressed with extcon_dev's
+                mutually_exclusive array.
+
 What:           /sys/class/extcon/.../name
 Date:           February 2012
 Contact:        MyungJoo Ham <myungjoo.ham@samsung.com>
@@ -73,3 +77,21 @@ Description:
                 state of cable "x" (integer between 0 and 31) of an extcon
                 device. The state value is either 0 (detached) or 1
                 (attached).
+
+What:           /sys/class/extcon/.../mutually_exclusive/...
+Date:           December 2011
+Contact:        MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+                Shows the relations of mutually exclusiveness. For example,
+                if the mutually_exclusive array of extcon_dev is
+                {0x3, 0x5, 0xC, 0x0}, the, the output is:
+                # ls mutually_exclusive/
+                0x3
+                0x5
+                0xc
+                #
+
+                Note that mutually_exclusive is a sub-directory of the extcon
+                device and the file names under the mutually_exclusive
+                directory show the mutually-exclusive sets, not the contents
+                of the files.
diff --git a/drivers/extcon/extcon_class.c b/drivers/extcon/extcon_class.c
index 403933bc3e9c..3bc4b8af46cf 100644
--- a/drivers/extcon/extcon_class.c
+++ b/drivers/extcon/extcon_class.c
@@ -72,6 +72,39 @@ static struct class_compat *switch_class;
 static LIST_HEAD(extcon_dev_list);
 static DEFINE_MUTEX(extcon_dev_list_lock);
 
+/**
+ * check_mutually_exclusive - Check if new_state violates mutually_exclusive
+ *                          condition.
+ * @edev:       the extcon device
+ * @new_state:  new cable attach status for @edev
+ *
+ * Returns 0 if nothing violates. Returns the index + 1 for the first
+ * violated condition.
+ */
+static int check_mutually_exclusive(struct extcon_dev *edev, u32 new_state)
+{
+        int i = 0;
+
+        if (!edev->mutually_exclusive)
+                return 0;
+
+        for (i = 0; edev->mutually_exclusive[i]; i++) {
+                int count = 0, j;
+                u32 correspondants = new_state & edev->mutually_exclusive[i];
+                u32 exp = 1;
+
+                for (j = 0; j < 32; j++) {
+                        if (exp & correspondants)
+                                count++;
+                        if (count > 1)
+                                return i + 1;
+                        exp <<= 1;
+                }
+        }
+
+        return 0;
+}
+
 static ssize_t state_show(struct device *dev, struct device_attribute *attr,
                           char *buf)
 {
@@ -100,7 +133,7 @@ static ssize_t state_show(struct device *dev, struct device_attribute *attr,
         return count;
 }
 
-void extcon_set_state(struct extcon_dev *edev, u32 state);
+int extcon_set_state(struct extcon_dev *edev, u32 state);
 static ssize_t state_store(struct device *dev, struct device_attribute *attr,
                            const char *buf, size_t count)
 {
@@ -112,7 +145,7 @@ static ssize_t state_store(struct device *dev, struct device_attribute *attr,
         if (ret == 0)
                 ret = -EINVAL;
         else
-                extcon_set_state(edev, state);
+                ret = extcon_set_state(edev, state);
 
         if (ret < 0)
                 return ret;
@@ -191,7 +224,7 @@ static ssize_t cable_state_store(struct device *dev,
  * Note that the notifier provides which bits are changed in the state
  * variable with the val parameter (second) to the callback.
  */
-void extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
+int extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
 {
         char name_buf[120];
         char state_buf[120];
@@ -206,6 +239,12 @@ void extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
         if (edev->state != ((edev->state & ~mask) | (state & mask))) {
                 u32 old_state = edev->state;
 
+                if (check_mutually_exclusive(edev, (edev->state & ~mask) |
+                                                   (state & mask))) {
+                        spin_unlock_irqrestore(&edev->lock, flags);
+                        return -EPERM;
+                }
+
                 edev->state &= ~mask;
                 edev->state |= state & mask;
 
@@ -247,6 +286,8 @@ void extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
                 /* No changes */
                 spin_unlock_irqrestore(&edev->lock, flags);
         }
+
+        return 0;
 }
 EXPORT_SYMBOL_GPL(extcon_update_state);
 
@@ -258,9 +299,9 @@ EXPORT_SYMBOL_GPL(extcon_update_state);
  * Note that notifier provides which bits are changed in the state
  * variable with the val parameter (second) to the callback.
  */
-void extcon_set_state(struct extcon_dev *edev, u32 state)
+int extcon_set_state(struct extcon_dev *edev, u32 state)
 {
-        extcon_update_state(edev, 0xffffffff, state);
+        return extcon_update_state(edev, 0xffffffff, state);
 }
 EXPORT_SYMBOL_GPL(extcon_set_state);
 
@@ -334,8 +375,7 @@ int extcon_set_cable_state_(struct extcon_dev *edev,
                 return -EINVAL;
 
         state = cable_state ? (1 << index) : 0;
-        extcon_update_state(edev, 1 << index, state);
-        return 0;
+        return extcon_update_state(edev, 1 << index, state);
 }
 EXPORT_SYMBOL_GPL(extcon_set_cable_state_);
 
@@ -511,6 +551,14 @@ static void extcon_cleanup(struct extcon_dev *edev, bool skip)
         if (!skip && get_device(edev->dev)) {
                 int index;
 
+                if (edev->mutually_exclusive && edev->max_supported) {
+                        for (index = 0; edev->mutually_exclusive[index];
+                             index++)
+                                kfree(edev->d_attrs_muex[index].attr.name);
+                        kfree(edev->d_attrs_muex);
+                        kfree(edev->attrs_muex);
+                }