3 files changed, 170 insertions, 0 deletions

diff --git a/Documentation/acpi/ssdt-overlays.txt b/Documentation/acpi/ssdt-overlays.txt
index 805025940248..c4b57badd0b7 100644
--- a/Documentation/acpi/ssdt-overlays.txt
+++ b/Documentation/acpi/ssdt-overlays.txt
@@ -89,3 +89,70 @@ cp ssdt.aml kernel/firmware/acpi
 # on top:
 find kernel | cpio -H newc --create > /boot/instrumented_initrd
 cat /boot/initrd >>/boot/instrumented_initrd
+
+== Loading ACPI SSDTs from EFI variables ==
+
+This is the preferred method, when EFI is supported on the platform, because it
+allows a persistent, OS independent way of storing the user defined SSDTs. There
+is also work underway to implement EFI support for loading user defined SSDTs
+and using this method will make it easier to convert to the EFI loading
+mechanism when that will arrive.
+
+In order to load SSDTs from an EFI variable the efivar_ssdt kernel command line
+parameter can be used. The argument for the option is the variable name to
+use. If there are multiple variables with the same name but with different
+vendor GUIDs, all of them will be loaded.
+
+In order to store the AML code in an EFI variable the efivarfs filesystem can be
+used. It is enabled and mounted by default in /sys/firmware/efi/efivars in all
+recent distribution.
+
+Creating a new file in /sys/firmware/efi/efivars will automatically create a new
+EFI variable. Updating a file in /sys/firmware/efi/efivars will update the EFI
+variable. Please note that the file name needs to be specially formatted as
+"Name-GUID" and that the first 4 bytes in the file (little-endian format)
+represent the attributes of the EFI variable (see EFI_VARIABLE_MASK in
+include/linux/efi.h). Writing to the file must also be done with one write
+operation.
+
+For example, you can use the following bash script to create/update an EFI
+variable with the content from a given file:
+
+#!/bin/sh -e
+
+while ! [ -z "$1" ]; do
+        case "$1" in
+        "-f") filename="$2"; shift;;
+        "-g") guid="$2"; shift;;
+        *) name="$1";;
+        esac
+        shift
+done
+
+usage()
+{
+        echo "Syntax: ${0##*/} -f filename [ -g guid ] name"
+        exit 1
+}
+
+[ -n "$name" -a -f "$filename" ] || usage
+
+EFIVARFS="/sys/firmware/efi/efivars"
+
+[ -d "$EFIVARFS" ] || exit 2
+
+if stat -tf $EFIVARFS | grep -q -v de5e81e4; then
+        mount -t efivarfs none $EFIVARFS
+fi
+
+# try to pick up an existing GUID
+[ -n "$guid" ] || guid=$(find "$EFIVARFS" -name "$name-*" | head -n1 | cut -f2- -d-)
+
+# use a randomly generated GUID
+[ -n "$guid" ] || guid="$(cat /proc/sys/kernel/random/uuid)"
+
+# efivarfs expects all of the data in one write
+tmp=$(mktemp)
+/bin/echo -ne "\007\000\000\000" | cat - $filename > $tmp
+dd if=$tmp of="$EFIVARFS/$name-$guid" bs=$(stat -c %s $tmp)
+rm $tmp
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82b42c958d1c..bbfb56fe7b92 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1185,6 +1185,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         Address Range Mirroring feature even if your box
                         doesn't support it.
 
+        efivar_ssdt=    [EFI; X86] Name of an EFI variable that contains an SSDT
+                        that is to be dynamically loaded by Linux. If there are
+                        multiple variables with the same name but with different
+                        vendor GUIDs, all of them will be loaded. See
+                        Documentation/acpi/ssdt-overlays.txt for details.
+
+
         eisa_irq_edge=  [PARISC,HW]
                         See header of drivers/parisc/eisa.c.
 
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 05509f3aaee8..8730fd475bf3 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -24,6 +24,9 @@
 #include <linux/of_fdt.h>
 #include <linux/io.h>
 #include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/acpi.h>
+#include <linux/ucs2_string.h>
 
 #include <asm/early_ioremap.h>
 
@@ -195,6 +198,96 @@ static void generic_ops_unregister(void)
         efivars_unregister(&generic_efivars);
 }
 
+#if IS_ENABLED(CONFIG_ACPI)
+#define EFIVAR_SSDT_NAME_MAX    16
+static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
+static int __init efivar_ssdt_setup(char *str)
+{
+        if (strlen(str) < sizeof(efivar_ssdt))
+                memcpy(efivar_ssdt, str, strlen(str));
+        else
+                pr_warn("efivar_ssdt: name too long: %s\n", str);
+        return 0;
+}
+__setup("efivar_ssdt=", efivar_ssdt_setup);
+
+static __init int efivar_ssdt_iter(efi_char16_t *name, efi_guid_t vendor,
+                                   unsigned long name_size, void *data)
+{
+        struct efivar_entry *entry;
+        struct list_head *list = data;
+        char utf8_name[EFIVAR_SSDT_NAME_MAX];
+        int limit = min_t(unsigned long, EFIVAR_SSDT_NAME_MAX, name_size);
+
+        ucs2_as_utf8(utf8_name, name, limit - 1);
+        if (strncmp(utf8_name, efivar_ssdt, limit) != 0)
+                return 0;
+
+        entry = kmalloc(sizeof(*entry), GFP_KERNEL);
+        if (!entry)
+                return 0;
+
+        memcpy(entry->var.VariableName, name, name_size);
+        memcpy(&entry->var.VendorGuid, &vendor, sizeof(efi_guid_t));
+
+        efivar_entry_add(entry, list);
+
+        return 0;
+}
+
+static __init int efivar_ssdt_load(void)
+{
+        LIST_HEAD(entries);
+        struct efivar_entry *entry, *aux;
+        unsigned long size;
+        void *data;
+        int ret;
+
+        ret = efivar_init(efivar_ssdt_iter, &entries, true, &entries);
+
+        list_for_each_entry_safe(entry, aux, &entries, list) {
+                pr_info("loading SSDT from variable %s-%pUl\n", efivar_ssdt,
+                        &entry->var.VendorGuid);
+
+                list_del(&entry->list);
+
+                ret = efivar_entry_size(entry, &size);
+                if (ret) {
+                        pr_err("failed to get var size\n");
+                        goto free_entry;
+                }
+
+                data = kmalloc(size, GFP_KERNEL);
+                if (!data)
+                        goto free_entry;
+
+                ret = efivar_entry_get(entry, NULL, &size, data);
+                if (ret) {
+                        pr_err("failed to get var data\n");
+                        goto free_data;
+                }
+
+                ret = acpi_load_table(data);
+                if (ret) {
+                        pr_err("failed to load table: %d\n", ret);
+                        goto free_data;
+                }
+
+                goto free_entry;
+
+free_data:
+                kfree(data);
+
+free_entry:
+                kfree(entry);
+        }
+
+        return ret;
+}
+#else
+static inline int efivar_ssdt_load(void) { return 0; }
+#endif
+
 /*
  * We register the efi subsystem with the firmware subsystem and the
  * efivars subsystem with the efi subsystem, if the system was booted with
@@ -218,6 +311,9 @@ static int __init efisubsys_init(void)
         if (error)
                 goto err_put;
 
+        if (efi_enabled(EFI_RUNTIME_SERVICES))
+                efivar_ssdt_load();
+
         error = sysfs_create_group(efi_kobj, &efi_subsys_attr_group);
         if (error) {
                 pr_err("efi: Sysfs attribute export failed with error %d.\n",