2 files changed, 108 insertions, 6 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index d141bdb3a7d4..7ef172c2a1d6 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -276,8 +276,10 @@ config ACPI_CUSTOM_DSDT
         depends on !STANDALONE
         default n 
         help
-          This option is to load a custom ACPI DSDT
-          If you don't know what that is, say N.
+          This option supports a custom DSDT by linking it into the kernel.
+          See Documentation/acpi/dsdt-override.txt
+
+          If unsure, say N.
 
 config ACPI_CUSTOM_DSDT_FILE
         string "Custom DSDT Table file to include"
@@ -287,6 +289,17 @@ 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
+          This option supports a custom DSDT by optionally loading it from initrd.
+          See Documentation/acpi/dsdt-override.txt
+
+          If you are not using this feature now, but may use it 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 c2c585366fa6..27ccd68b8f46 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -91,6 +91,10 @@ static DEFINE_SPINLOCK(acpi_res_lock);
 #define OSI_STRING_LENGTH_MAX 64        /* arbitrary */
 static char osi_additional_string[OSI_STRING_LENGTH_MAX];
 
+#ifdef CONFIG_ACPI_CUSTOM_DSDT_INITRD
+static int acpi_no_initrd_override;
+#endif
+
 /*
  * "Ode to _OSI(Linux)"
  *
@@ -329,6 +333,67 @@ 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 "Checking initramfs for custom DSDT");
+
+        /*
+         * 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.
+         * A static/init firmware infrastructure doesn't exist yet...
+         */
+        if (vfs_stat(ramfs_dsdt_name, &stat) < 0)
+                return ret;
+
+        len = stat.size;
+        /* check especially against empty files */
+        if (len <= 4) {
+                printk(KERN_ERR PREFIX "Failed: DSDT only %lu bytes.\n", len);
+                return ret;
+        }
+
+        firmware_file = filp_open(ramfs_dsdt_name, O_RDONLY, 0);
+        if (IS_ERR(firmware_file)) {
+                printk(KERN_ERR PREFIX "Failed to open %s.\n", ramfs_dsdt_name);
+                return ret;
+        }
+
+        dsdt_buffer = kmalloc(len, GFP_ATOMIC);
+        if (!dsdt_buffer) {
+                printk(KERN_ERR PREFIX "Failed to allocate %lu bytes.\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(KERN_ERR PREFIX "Failed to read %lu bytes from %s.\n",
+                        len, ramfs_dsdt_name);
+                ACPI_FREE(dsdt_buffer);
+                goto err;
+        }
+
+        printk(KERN_INFO PREFIX "Found %lu byte DSDT in %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)
@@ -336,17 +401,41 @@ 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) &&
+            !acpi_no_initrd_override) {
+                struct acpi_table_header *initrd_table;
+
+                initrd_table = acpi_find_dsdt_initrd();
+                if (initrd_table)
+                        *new_table = initrd_table;
+        }
+#endif
+        if (*new_table != NULL) {
+                printk(KERN_WARNING PREFIX "Override [%4.4s-%8.8s], "
+                           "this is unsafe: tainting kernel\n",
+                       existing_table->signature,
+                       existing_table->oem_table_id);
+                add_taint(TAINT_OVERRIDDEN_ACPI_TABLE);
+        }
         return AE_OK;
 }
 
+#ifdef CONFIG_ACPI_CUSTOM_DSDT_INITRD
+int __init acpi_no_initrd_override_setup(char *s)
+{
+        acpi_no_initrd_override = 1;
+        return 1;
+}
+__setup("acpi_no_initrd_override", acpi_no_initrd_override_setup);
+#endif
+
 static irqreturn_t acpi_irq(int irq, void *dev_id)
 {
         u32 handled;