Add memrt kernel driver.

Introduce the driver/android/things path to store kernel drivers related
to the Android Things platform.

The first of which is the memrt UIO driver. It exposes a block of shared
memory that is used to implement an in-memory serial channel. The
location and size of this block is read from the device tree for
flexability.

Test: Running locally with non-committed changes.
Change-Id: I3178e3a96b394292b4fabde6abc0e41c18db85a1

6 files changed, 101 insertions, 0 deletions

diff --git a/drivers/android/Kconfig b/drivers/android/Kconfig
index 01de42c8b74b..2804034a82b6 100644
--- a/drivers/android/Kconfig
+++ b/drivers/android/Kconfig
@@ -1,5 +1,7 @@
 menu "Android"
 
+source "drivers/android/things/Kconfig"
+
 config ANDROID
 	bool "Android Drivers"
 	---help---
diff --git a/drivers/android/Makefile b/drivers/android/Makefile
index a01254c43ee3..9b5c7a538e0c 100644
--- a/drivers/android/Makefile
+++ b/drivers/android/Makefile
@@ -1,3 +1,5 @@
+obj-y += things/
+
 ccflags-y += -I$(src)			# needed for trace events
 
 obj-$(CONFIG_ANDROID_BINDER_IPC)	+= binder.o binder_alloc.o
diff --git a/drivers/android/things/Kconfig b/drivers/android/things/Kconfig
new file mode 100644
index 000000000000..6a0ffbdd48cf
--- /dev/null
+++ b/drivers/android/things/Kconfig
@@ -0,0 +1,6 @@
+config ANDROIDTHINGS_REALTIME
+	bool "Build drivers for realtime subsystem of Android Things."
+	select UIO
+	help
+	 Say Yes here to build shared memory based drivers to communicate
+	 between Realtime process and Android.
diff --git a/drivers/android/things/Makefile b/drivers/android/things/Makefile
new file mode 100644
index 000000000000..3dc06084c50f
--- /dev/null
+++ b/drivers/android/things/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_ANDROIDTHINGS_REALTIME) += realtime/
diff --git a/drivers/android/things/realtime/Makefile b/drivers/android/things/realtime/Makefile
new file mode 100644
index 000000000000..b22c0ae84461
--- /dev/null
+++ b/drivers/android/things/realtime/Makefile
@@ -0,0 +1 @@
+obj-y += memrt-uio.o
diff --git a/drivers/android/things/realtime/memrt-uio.c b/drivers/android/things/realtime/memrt-uio.c
new file mode 100644
index 000000000000..84fd30a90761
--- /dev/null
+++ b/drivers/android/things/realtime/memrt-uio.c
@@ -0,0 +1,89 @@
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_device.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/uio_driver.h>
+
+#define DEVICE_NAME "memrt"
+#define DEVICE_VERSION "1.0"
+
+static DEFINE_SPINLOCK(is_open_lock);
+static bool is_open;  // Initialized to false by kernel.
+
+static const struct of_device_id memrt_match[] = {
+	{ .compatible = "android,memrt", },
+	{}
+};
+
+static int open(struct uio_info *uio, struct inode *node)
+{
+	spin_lock(&is_open_lock);
+	if (is_open)
+		return -EBUSY;
+	is_open = true;
+	spin_unlock(&is_open_lock);
+	return 0;
+}
+
+static int close(struct uio_info *uio, struct inode *node)
+{
+	spin_lock(&is_open_lock);
+	is_open = false;
+	spin_unlock(&is_open_lock);
+	return 0;
+}
+
+static int probe(struct platform_device *platform)
+{
+	const struct of_device_id *match = NULL;
+	struct uio_info *uio = NULL;
+	u64 size = 0;
+
+	match = of_match_device(memrt_match, &platform->dev);
+	if (!match)
+		return -EINVAL;
+
+	uio = devm_kzalloc(&platform->dev, sizeof(struct uio_info), GFP_KERNEL);
+	uio->name = DEVICE_NAME;
+	uio->version = DEVICE_VERSION;
+	uio->irq = UIO_IRQ_NONE;
+	uio->open = open;
+	uio->release = close;
+
+	uio->mem[0].memtype = UIO_MEM_PHYS;
+	uio->mem[0].addr =
+		of_translate_address(platform->dev.of_node,
+				     of_get_address(platform->dev.of_node, 0,
+						    &size, NULL));
+	uio->mem[0].size = (resource_size_t)size;
+
+	if (!uio->mem[0].addr || uio->mem[0].addr == OF_BAD_ADDR) {
+		pr_err("MemRt failed to map shared memory.\n");
+		return -ENOMEM;
+	}
+
+	return uio_register_device(&platform->dev, uio);
+}
+
+MODULE_DEVICE_TABLE(of, memrt_match);
+
+static struct platform_driver memrt_driver = {
+	.probe = probe,
+	.driver = {
+		.name = DEVICE_NAME,
+		.of_match_table = memrt_match,
+	},
+};
+
+module_platform_driver(memrt_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Ed Coyne, Google Inc.");
+MODULE_DESCRIPTION("Shared memory serial channel between processors.");