[PATCH] ACPI: Add new sysfs interface to export device description

[Lance Ortiz]

Add support to export the device description obtained from the ACPI _STR
method, if one exists for a device, to user-space via a sysfs interface.
This new interface provides a standard and platform neutral way for users
to obtain the description text stored in the ACPI _STR method.  If no
_STR method exists for the device, no sysfs 'description' file will be
created.  The 'description' file will be located in the /sys/devices/
directory using the device's path.

/sys/device/<bus>/<bridge path>/<device path>.../firmware_node/description

Example:

/sys/devices/pci0000:00/0000:00.07.0/0000:0e:00.0/firmware_node/description

It can also be located using the ACPI device path, for example:

/sys/devices/LNXSYSTM:00/device:00/ACPI0004:00/PNP0A08:00/device:13/device:15/description
/sys/devices/LNXSYSTM:00/device:00/ACPI0004:00/ACPI0004:01/ACPI0007:02/description

Execute the 'cat' command on the 'description' file to obtain the
description string for that device.

This patch also includes documentation describing how the new sysfs
interface works

Signed-off-by: Lance Ortiz <lance.ortiz@xxxxxx>
---
 .../ABI/testing/sysfs-devices-firmware_node        |   17 ++++++
 drivers/acpi/scan.c                                |   58 +++++++++++++++++++-
 include/acpi/acpi_bus.h                            |    1 +
 3 files changed, 74 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-devices-firmware_node

diff --git a/Documentation/ABI/testing/sysfs-devices-firmware_node b/Documentation/ABI/testing/sysfs-devices-firmware_node
new file mode 100644
index 0000000..46badc9
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-firmware_node
@@ -0,0 +1,17 @@
+What:		/sys/devices/.../firmware_node/
+Date:		September 2012
+Contact:	<>
+Description:
+		The /sys/devices/.../firmware_node directory contains attributes
+		allowing the user space to check and modify some firmware
+		related properties of given device.
+
+What:		/sys/devices/.../firmware_node/description
+Date:		September 2012
+Contact:	Lance Ortiz <lance.ortiz@xxxxxx>
+Description:
+		The /sys/devices/.../firmware/description attribute contains a string
+		that describes the device as provided by the _STR method in the ACPI
+		namespace.  This attribute is read-only.  If the device does not have
+		an _STR method associated with it in the ACPI namespace, this
+		attribute is not present.
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index c8a1f3b..c9c91e1 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -10,6 +10,7 @@
 #include <linux/signal.h>
 #include <linux/kthread.h>
 #include <linux/dmi.h>
+#include <linux/nls.h>
 
 #include <acpi/acpi_drivers.h>
 
@@ -192,8 +193,38 @@ end:
 }
 static DEVICE_ATTR(path, 0444, acpi_device_path_show, NULL);
 
+/* sysfs file that shows description text from the ACPI _STR method */
+static ssize_t description_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf) {
+	struct acpi_device *acpi_dev = to_acpi_device(dev);
+	int result;
+
+	if (acpi_dev->pnp.str_obj == NULL) {
+		result = sprintf(buf, "No Description\n");
+		goto end;
+	}
+
+	/*
+	 * The _STR object contains a Unicode identifier for a device.
+	 * We need to convert to utf-8 so it can be displayed.
+	 */
+	result = utf16s_to_utf8s(
+		(wchar_t *)acpi_dev->pnp.str_obj->buffer.pointer,
+		acpi_dev->pnp.str_obj->buffer.length,
+		UTF16_LITTLE_ENDIAN, buf,
+		PAGE_SIZE);
+
+	buf[result++] = '\n';
+
+end:
+	return result;
+}
+static DEVICE_ATTR(description, 0444, description_show, NULL);
+
 static int acpi_device_setup_files(struct acpi_device *dev)
 {
+	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
 	acpi_status status;
 	acpi_handle temp;
 	int result = 0;
@@ -217,6 +248,21 @@ static int acpi_device_setup_files(struct acpi_device *dev)
 			goto end;
 	}
 
+	/*
+	 * If device has _STR, 'description' file is created
+	 */
+	status = acpi_get_handle(dev->handle, "_STR", &temp);
+	if (ACPI_SUCCESS(status)) {
+		status = acpi_evaluate_object(dev->handle, "_STR",
+					NULL, &buffer);
+		if (ACPI_FAILURE(status))
+			buffer.pointer = NULL;
+		dev->pnp.str_obj = buffer.pointer;
+		result = device_create_file(&dev->dev, &dev_attr_description);
+		if (result)
+			goto end;
+	}
+
         /*
          * If device has _EJ0, 'eject' file is created that is used to trigger
          * hot-removal function from userland.
@@ -234,8 +280,16 @@ static void acpi_device_remove_files(struct acpi_device *dev)
 	acpi_handle temp;
 
 	/*
-	 * If device has _EJ0, 'eject' file is created that is used to trigger
-	 * hot-removal function from userland.
+	 * If device has _STR, remove 'description' file
+	 */
+	status = acpi_get_handle(dev->handle, "_STR", &temp);
+	if (ACPI_SUCCESS(status)) {
+		if (dev->pnp.str_obj != NULL)
+			kfree(dev->pnp.str_obj);
+		device_remove_file(&dev->dev, &dev_attr_description);
+	}
+	/*
+	 * If device has _EJ0, remove 'eject' file.
 	 */
 	status = acpi_get_handle(dev->handle, "_EJ0", &temp);
 	if (ACPI_SUCCESS(status))
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 9e6e1c6..12172d5 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -209,6 +209,7 @@ struct acpi_device_pnp {
 	struct list_head ids;		/* _HID and _CIDs */
 	acpi_device_name device_name;	/* Driver-determined */
 	acpi_device_class device_class;	/*        "          */
+	union acpi_object *str_obj;	/* unicode string for _STR method */
 };
 
 #define acpi_device_bid(d)	((d)->pnp.bus_id)
-- 
1.7.7.6

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