[PATCH 1/5] ACPI: sysfs: convert utf-16 from _STR to utf-8 only once

[Thomas Weißschuh <linux@xxxxxxxxxxxxxx>]

The ACPI _STR method returns an UTF-16 string that is converted to utf-8
before printing it in sysfs.
Currently this conversion is performed every time the "description"
sysfs attribute is read, which is not necessary.

Only perform the conversion once and cache the result.

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
 drivers/acpi/device_sysfs.c | 63 ++++++++++++++++++++++++++++-----------------
 include/acpi/acpi_bus.h     |  2 +-
 2 files changed, 40 insertions(+), 25 deletions(-)

diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
index 23373faa35ec..4bedbe8f57ed 100644
--- a/drivers/acpi/device_sysfs.c
+++ b/drivers/acpi/device_sysfs.c
@@ -439,24 +439,11 @@ static ssize_t description_show(struct device *dev,
 				char *buf)
 {
 	struct acpi_device *acpi_dev = to_acpi_device(dev);
-	int result;
 
-	if (acpi_dev->pnp.str_obj == NULL)
+	if (acpi_dev->pnp.str == NULL)
 		return 0;
 
-	/*
-	 * 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 - 1);
-
-	buf[result++] = '\n';
-
-	return result;
+	return sysfs_emit("%s\n", acpi_dev->pnp.str);
 }
 static DEVICE_ATTR_RO(description);
 
@@ -507,14 +494,46 @@ static ssize_t status_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(status);
 
+static const char *acpi_device_str(struct acpi_device *dev)
+{
+	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
+	union acpi_object *str_obj;
+	acpi_status status;
+	const char *ret;
+	char buf[512];
+	int result;
+
+	if (!acpi_has_method(dev->handle, "_STR"))
+		return NULL;
+
+	status = acpi_evaluate_object(dev->handle, "_STR",
+				      NULL, &buffer);
+	if (ACPI_FAILURE(status))
+		return NULL;
+
+	str_obj = buffer.pointer;
+	/*
+	 * 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 *)str_obj->buffer.pointer,
+				 str_obj->buffer.length,
+				 UTF16_LITTLE_ENDIAN,
+				 buf, sizeof(buf) - 1);
+	buf[result++] = '\0';
+
+	ret = kstrdup(buf, GFP_KERNEL);
+	kfree(buffer.pointer);
+
+	return ret;
+}
+
 /**
  * acpi_device_setup_files - Create sysfs attributes of an ACPI device.
  * @dev: ACPI device object.
  */
 int acpi_device_setup_files(struct acpi_device *dev)
 {
-	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
-	acpi_status status;
 	int result = 0;
 
 	/*
@@ -539,12 +558,8 @@ int acpi_device_setup_files(struct acpi_device *dev)
 	/*
 	 * If device has _STR, 'description' file is created
 	 */
-	if (acpi_has_method(dev->handle, "_STR")) {
-		status = acpi_evaluate_object(dev->handle, "_STR",
-					NULL, &buffer);
-		if (ACPI_FAILURE(status))
-			buffer.pointer = NULL;
-		dev->pnp.str_obj = buffer.pointer;
+	dev->pnp.str = acpi_device_str(dev);
+	if (dev->pnp.str) {
 		result = device_create_file(&dev->dev, &dev_attr_description);
 		if (result)
 			goto end;
@@ -618,7 +633,7 @@ void acpi_device_remove_files(struct acpi_device *dev)
 	 * If device has _STR, remove 'description' file
 	 */
 	if (acpi_has_method(dev->handle, "_STR")) {
-		kfree(dev->pnp.str_obj);
+		kfree(dev->pnp.str);
 		device_remove_file(&dev->dev, &dev_attr_description);
 	}
 	/*
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 1a4dfd7a1c4a..32e3105c9ece 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -254,7 +254,7 @@ 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 */
+	const char *str;		/* _STR */
 };
 
 #define acpi_device_bid(d)	((d)->pnp.bus_id)

-- 
2.45.2