Add Lenovo IdeaPad Y470/Y570 hack

Warning: this is a very ugly hack, I do not know whether it works or not. It may
be unstable and does very unusual things.

acpi-handle-hack.c

@@ -0,0 +1,85 @@
+/**
+ * Very ugly hack to work around a wrongly detected ACPI handle, see
+ * https://bugzilla.kernel.org/show_bug.cgi?id=42696
+ */
+
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/acpi.h>
+#include <linux/dmi.h>
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Dirty ACPI handle hack for Lenovo IdeaPad Y[45]70");
+MODULE_AUTHOR("Peter Lekensteyn <lekensteyn@gmail.com>");
+MODULE_VERSION("0.0.1");
+
+static struct pci_dev *dis_dev;
+static acpi_handle orig_handle;
+
+/**
+ * Returns true if the system needs an ACPI handle hack
+ */
+static bool __init need_acpi_handle_hack(void) {
+	return dmi_match(DMI_PRODUCT_VERSION, "Lenovo IdeaPad Y470") ||
+		dmi_match(DMI_PRODUCT_VERSION, "Lenovo IdeaPad Y570");
+}
+
+static struct pci_dev __init *get_discrete_device(void) {
+	struct pci_dev *pdev = NULL;
+	int class = PCI_CLASS_DISPLAY_VGA << 8;
+	while ((pdev = pci_get_class(class, pdev)) != NULL) {
+		if (pdev->vendor != PCI_VENDOR_ID_INTEL) {
+			return pdev;
+		}
+	}
+	return NULL;
+}
+
+/**
+ * Very ugly hack to set the ACPI handle, do not use this as exemplary code!
+ */
+static void dev_set_acpi_handle(struct pci_dev *pdev, acpi_handle handle) {
+	pdev->dev.archdata.acpi_handle = handle;
+}
+
+static int __init hack_apply(void) {
+	acpi_handle tmp_handle, new_handle;
+	struct acpi_buffer buf = { ACPI_ALLOCATE_BUFFER, NULL };
+	if (!need_acpi_handle_hack()) {
+		printk(KERN_ERR "Machine does not need ACPI handle hack\n");
+		return -ENODEV;
+	}
+	dis_dev = get_discrete_device();
+	if (!dis_dev) {
+		printk(KERN_ERR "No discrete video card found\n");
+		return -ENODEV;
+	}
+	orig_handle = DEVICE_ACPI_HANDLE(&dis_dev->dev);
+	if (!orig_handle) {
+		printk(KERN_ERR "No ACPI handle found for discrete\n");
+		return -ENODEV;
+	}
+	acpi_get_name(orig_handle, ACPI_SINGLE_NAME, &buf);
+	if (strcmp((char *)buf.pointer, "PEGP") == 0) {
+		printk(KERN_ERR "Handle has already be changed\n");
+		return -ENODEV;
+	}
+	/* \_SB.PCI0.PEG0.VGA_ -> \_SB.PCI0.PEG0.PEGP */
+	acpi_get_parent(orig_handle, &tmp_handle);
+	acpi_get_handle(tmp_handle, "PEGP", &new_handle);
+	printk(KERN_INFO "Setting new ACPI handle for discrete video card\n");
+	dev_set_acpi_handle(dis_dev, new_handle);
+	pci_dev_put(dis_dev);
+	return 0;
+}
+
+static void __exit hack_undo(void) {
+	if (orig_handle) {
+		printk(KERN_INFO "Restoring original ACPI handle for discrete"
+			" video card\n");
+		dev_set_acpi_handle(dis_dev, orig_handle);
+	}
+}
+
+module_init(hack_apply);
+module_exit(hack_undo);