2 files changed, 86 insertions, 4 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index ccf6ea95f68c..0442ae153a24 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -274,6 +274,23 @@ config ACPI_CUSTOM_DSDT_FILE
           Enter the full path name to the file which includes the AmlCode
           declaration.
 
+config ACPI_CUSTOM_DSDT_INITRD
+        bool "Read Custom DSDT from initramfs"
+        depends on BLK_DEV_INITRD
+        default n
+        help
+          The DSDT (Differentiated System Description Table) often needs to be
+          overridden because of broken BIOS implementations. If this feature is
+          activated you will be able to provide a customized DSDT by adding it
+          to your initramfs. If your mkinitrd tool does not support this feature
+          a script is provided in the documentation. For more details see
+          <file:Documentation/dsdt-initrd.txt> or <http://gaugusch.at/kernel.shtml>.
+          If there is no table found, it will fall-back to the custom DSDT
+          in-kernel (if activated) or to the DSDT from the BIOS.
+
+          Even if you do not need a new one at the moment, you may want to use a
+          better DSDT later. It is safe to say Y here.
+
 config ACPI_BLACKLIST_YEAR
         int "Disable ACPI for systems before Jan 1st this year" if X86_32
         default 0
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index e53fb516f9d4..131936e7ff17 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -312,6 +312,66 @@ acpi_os_predefined_override(const struct acpi_predefined_names *init_val,
         return AE_OK;
 }
 
+#ifdef CONFIG_ACPI_CUSTOM_DSDT_INITRD
+struct acpi_table_header *acpi_find_dsdt_initrd(void)
+{
+        struct file *firmware_file;
+        mm_segment_t oldfs;
+        unsigned long len, len2;
+        struct acpi_table_header *dsdt_buffer, *ret = NULL;
+        struct kstat stat;
+        char *ramfs_dsdt_name = "/DSDT.aml";
+
+        printk(KERN_INFO PREFIX "Looking for DSDT in initramfs... ");
+
+        /*
+         * Never do this at home, only the user-space is allowed to open a file.
+         * The clean way would be to use the firmware loader. But this code must be run
+         * before there is any userspace available. So we need a static/init firmware
+         * infrastructure, which doesn't exist yet...
+         */
+        if (vfs_stat(ramfs_dsdt_name, &stat) < 0) {
+                printk("not found.\n");
+                return ret;
+        }
+
+        len = stat.size;
+        /* check especially against empty files */
+        if (len <= 4) {
+                printk("error, file is too small: only %lu bytes.\n", len);
+                return ret;
+        }
+
+        firmware_file = filp_open(ramfs_dsdt_name, O_RDONLY, 0);
+        if (IS_ERR(firmware_file)) {
+                printk("error, could not open file %s.\n", ramfs_dsdt_name);
+                return ret;
+        }
+
+        dsdt_buffer = ACPI_ALLOCATE(len);
+        if (!dsdt_buffer) {
+                printk("error when allocating %lu bytes of memory.\n", len);
+                goto err;
+        }
+
+        oldfs = get_fs();
+        set_fs(KERNEL_DS);
+        len2 = vfs_read(firmware_file, (char __user *)dsdt_buffer, len, &firmware_file->f_pos);
+        set_fs(oldfs);
+        if (len2 < len) {
+                printk("error trying to read %lu bytes from %s.\n", len, ramfs_dsdt_name);
+                ACPI_FREE(dsdt_buffer);
+                goto err;
+        }
+
+        printk("successfully read %lu bytes from %s.\n", len, ramfs_dsdt_name);
+        ret = dsdt_buffer;
+err:
+        filp_close(firmware_file, NULL);
+        return ret;
+}
+#endif
+
 acpi_status
 acpi_os_table_override(struct acpi_table_header * existing_table,
                        struct acpi_table_header ** new_table)
@@ -319,13 +379,18 @@ acpi_os_table_override(struct acpi_table_header * existing_table,
         if (!existing_table || !new_table)
                 return AE_BAD_PARAMETER;
 
+        *new_table = NULL;
+
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
         if (strncmp(existing_table->signature, "DSDT", 4) == 0)
                 *new_table = (struct acpi_table_header *)AmlCode;
-        else
-                *new_table = NULL;
-#else
-        *new_table = NULL;
+#endif
+#ifdef CONFIG_ACPI_CUSTOM_DSDT_INITRD
+        if (strncmp(existing_table->signature, "DSDT", 4) == 0) {
+                struct acpi_table_header *initrd_table = acpi_find_dsdt_initrd();
+                if (initrd_table)
+                        *new_table = initrd_table;
+        }
 #endif
         return AE_OK;
 }