platform/x86: dell-wmi-descriptor: split WMI descriptor into it's own driver

All communication on individual GUIDs should occur in separate drivers.
Allowing a driver to communicate with the bus to another GUID is just
a hack that discourages drivers to adopt the bus model.

The information found from the WMI descriptor driver is now exported
for use by other drivers.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/dell-wmi-descriptor.c

@@ -0,0 +1,170 @@
+/*
+ * Dell WMI descriptor driver
+ *
+ * Copyright (C) 2017 Dell Inc. All Rights Reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License version 2 as published
+ *  by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/acpi.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/wmi.h>
+#include "dell-wmi-descriptor.h"
+
+struct descriptor_priv {
+	struct list_head list;
+	u32 interface_version;
+	u32 size;
+};
+static LIST_HEAD(wmi_list);
+static DEFINE_MUTEX(list_mutex);
+
+bool dell_wmi_get_interface_version(u32 *version)
+{
+	struct descriptor_priv *priv;
+	bool ret = false;
+
+	mutex_lock(&list_mutex);
+	priv = list_first_entry_or_null(&wmi_list,
+					struct descriptor_priv,
+					list);
+	if (priv) {
+		*version = priv->interface_version;
+		ret = true;
+	}
+	mutex_unlock(&list_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dell_wmi_get_interface_version);
+
+bool dell_wmi_get_size(u32 *size)
+{
+	struct descriptor_priv *priv;
+	bool ret = false;
+
+	mutex_lock(&list_mutex);
+	priv = list_first_entry_or_null(&wmi_list,
+					struct descriptor_priv,
+					list);
+	if (priv) {
+		*size = priv->size;
+		ret = true;
+	}
+	mutex_unlock(&list_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dell_wmi_get_size);
+
+/*
+ * Descriptor buffer is 128 byte long and contains:
+ *
+ *       Name             Offset  Length  Value
+ * Vendor Signature          0       4    "DELL"
+ * Object Signature          4       4    " WMI"
+ * WMI Interface Version     8       4    <version>
+ * WMI buffer length        12       4    <length>
+ */
+static int dell_wmi_descriptor_probe(struct wmi_device *wdev)
+{
+	union acpi_object *obj = NULL;
+	struct descriptor_priv *priv;
+	u32 *buffer;
+	int ret;
+
+	obj = wmidev_block_query(wdev, 0);
+	if (!obj) {
+		dev_err(&wdev->dev, "failed to read Dell WMI descriptor\n");
+		ret = -EIO;
+		goto out;
+	}
+
+	if (obj->type != ACPI_TYPE_BUFFER) {
+		dev_err(&wdev->dev, "Dell descriptor has wrong type\n");
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Although it's not technically a failure, this would lead to
+	 * unexpected behavior
+	 */
+	if (obj->buffer.length != 128) {
+		dev_err(&wdev->dev,
+			"Dell descriptor buffer has unexpected length (%d)\n",
+			obj->buffer.length);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	buffer = (u32 *)obj->buffer.pointer;
+
+	if (strncmp(obj->string.pointer, "DELL WMI", 8) != 0) {
+		dev_err(&wdev->dev, "Dell descriptor buffer has invalid signature (%8ph)\n",
+			buffer);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (buffer[2] != 0 && buffer[2] != 1)
+		dev_warn(&wdev->dev, "Dell descriptor buffer has unknown version (%lu)\n",
+			(unsigned long) buffer[2]);
+
+	priv = devm_kzalloc(&wdev->dev, sizeof(struct descriptor_priv),
+	GFP_KERNEL);
+
+	priv->interface_version = buffer[2];
+	priv->size = buffer[3];
+	ret = 0;
+	dev_set_drvdata(&wdev->dev, priv);
+	mutex_lock(&list_mutex);
+	list_add_tail(&priv->list, &wmi_list);
+	mutex_unlock(&list_mutex);
+
+	dev_dbg(&wdev->dev, "Detected Dell WMI interface version %lu and buffer size %lu\n",
+		(unsigned long) priv->interface_version,
+		(unsigned long) priv->size);
+
+out:
+	kfree(obj);
+	return ret;
+}
+
+static int dell_wmi_descriptor_remove(struct wmi_device *wdev)
+{
+	struct descriptor_priv *priv = dev_get_drvdata(&wdev->dev);
+
+	mutex_lock(&list_mutex);
+	list_del(&priv->list);
+	mutex_unlock(&list_mutex);
+	return 0;
+}
+
+static const struct wmi_device_id dell_wmi_descriptor_id_table[] = {
+	{ .guid_string = DELL_WMI_DESCRIPTOR_GUID },
+	{ },
+};
+
+static struct wmi_driver dell_wmi_descriptor_driver = {
+	.driver = {
+		.name = "dell-wmi-descriptor",
+	},
+	.probe = dell_wmi_descriptor_probe,
+	.remove = dell_wmi_descriptor_remove,
+	.id_table = dell_wmi_descriptor_id_table,
+};
+
+module_wmi_driver(dell_wmi_descriptor_driver);
+
+MODULE_ALIAS("wmi:" DELL_WMI_DESCRIPTOR_GUID);
+MODULE_AUTHOR("Mario Limonciello <mario.limonciello@dell.com>");
+MODULE_DESCRIPTION("Dell WMI descriptor driver");
+MODULE_LICENSE("GPL");