greybus: bundle: add state sysfs file

A bundle has a state file, that is managed by the endo userspace
process.  This file can be written to and any process that is polling on
the file will be woken up and can read the new value.  It's a "cheap"
IPC for programs that are not allowed to do anything other than
read/write to kernel sysfs files.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

diff --git a/drivers/staging/greybus/Documentation/sysfs-bus-greybus b/drivers/staging/greybus/Documentation/sysfs-bus-greybus
index 4b511dbff0da9af4a9d35d8723fe41090bb5bf72..ab728a46e6575ac5863eedba81bcba623f89af24 100644 (file)
--- a/drivers/staging/greybus/Documentation/sysfs-bus-greybus
+++ b/drivers/staging/greybus/Documentation/sysfs-bus-greybus
@@ -113,3 +113,16 @@ KernelVersion:     4.XX
 Contact:       Greg Kroah-Hartman <greg@kroah.com>
 Description:
                The device id of a Greybus bundle.
+
+What:          /sys/bus/greybus/device/.../state
+Date:          October 2015
+KernelVersion: 4.XX
+Contact:       Greg Kroah-Hartman <greg@kroah.com>
+Description:
+               A bundle has a state that is managed by the userspace
+               Endo process.  This file allows that Endo to signal
+               other Android HALs that the state of the bundle has
+               changed to a specific value.  When written to, any
+               process watching the file will be woken up, and the new
+               value can be read. It's a "poor-man's IPC", yes, but
+               simplifies the Android userspace code immensely.

diff --git a/drivers/staging/greybus/bundle.c b/drivers/staging/greybus/bundle.c
index 3f1aa6490e48b7a6c96910ea3f8e1a47d03af868..e7b2199f39b4d6d7886bd3e6ddcea771128b7681 100644 (file)
--- a/drivers/staging/greybus/bundle.c
+++ b/drivers/staging/greybus/bundle.c
@@ -1,8 +1,8 @@
 /*
  * Greybus bundles
  *
- * Copyright 2014 Google Inc.
- * Copyright 2014 Linaro Ltd.
+ * Copyright 2014-2015 Google Inc.
+ * Copyright 2014-2015 Linaro Ltd.
  *
  * Released under the GPLv2 only.
  */
@@ -31,9 +31,41 @@ static ssize_t class_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(class);
 
+static ssize_t state_show(struct device *dev, struct device_attribute *attr,
+                         char *buf)
+{
+       struct gb_bundle *bundle = to_gb_bundle(dev);
+
+       if (bundle->state == NULL)
+               return sprintf(buf, "\n");
+
+       return sprintf(buf, "%s\n", bundle->state);
+}
+
+static ssize_t state_store(struct device *dev, struct device_attribute *attr,
+                          const char *buf, size_t size)
+{
+       struct gb_bundle *bundle = to_gb_bundle(dev);
+
+       kfree(bundle->state);
+       bundle->state = kzalloc(size + 1, GFP_KERNEL);
+       if (!bundle->state)
+               return -ENOMEM;
+
+       memcpy(bundle->state, buf, size);
+
+       /* Tell userspace that the file contents changed */
+       sysfs_notify(&bundle->dev.kobj, NULL, "state");
+
+       return size;
+}
+static DEVICE_ATTR_RW(state);
+
+
 static struct attribute *bundle_attrs[] = {
        &dev_attr_device_id.attr,
        &dev_attr_class.attr,
+       &dev_attr_state.attr,
        NULL,
 };
 
@@ -43,6 +75,7 @@ static void gb_bundle_release(struct device *dev)
 {
        struct gb_bundle *bundle = to_gb_bundle(dev);
 
+       kfree(bundle->state);
        kfree(bundle);
 }
 

diff --git a/drivers/staging/greybus/bundle.h b/drivers/staging/greybus/bundle.h
index 3265a008e5df5384bc1048c450cf8c719701f074..5c12c72ddcec86e99948c29a1a933dfeec8d6115 100644 (file)
--- a/drivers/staging/greybus/bundle.h
+++ b/drivers/staging/greybus/bundle.h
@@ -20,6 +20,7 @@ struct gb_bundle {
        u8                      class;
        u8                      device_id;
        struct list_head        connections;
+       u8                      *state;
 
        struct list_head        links;  /* interface->bundles */
 };