Re: [RFC] Include ACPI DSDT from INITRD patch into mainline

[Sergey Vlasov]

On Sat, 02 Dec 2006 11:30:32 +0100 Arjan van de Ven wrote:

> On Fri, 2006-12-01 at 13:36 -0500, Ben Collins wrote:
> > I'd be willing to bet that most distros have this patch in their kernel.
> > One of those things we can't really live without.
> >
> > What I haven't understood is why it isn't included in the mainline
> > kernel yet.
>
> it's not that hard ;)
>
> replacing the DSDT code *while it's live* is just a bad idea.

But the suggested patch does not do this.

> The kernel already has a facility to override the DSDT, but that one
> does it *from the start*. Sounds like that one should be used or
> maybe enhanced a little to make it more distro friendly if something
> is lacking.

The patch replaces the DSDT with the binary from initramfs in the same
acpi_os_table_override() function as the currently available
CONFIG_ACPI_CUSTOM_DSDT does:

@@ -226,13 +291,20 @@ acpi_os_table_override(struct acpi_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;
+                       acpi_must_unregister_table = TRUE;
+               }
+       }
 #endif
        return AE_OK;
 }

However, this patch slightly changes initialization order of some
kernel parts:

 - The call to populate_rootfs() is moved before calls to
   smp_prepare_cpus(max_cpus), do_pre_smp_initcalls(), smp_init(),
   sched_init_smp() and cpuset_init_smp().

 - The call to acpi_early_init() is moved from start_kernel() (where
   it is done just before rest_init()) to rest_init(), where it is now
   preceded by lock_kernel(), set_cpus_allowed(current, CPU_MASK_ALL),
   child_reaper = current and the moved populate_rootfs().

Not sure if this reordering is safe in theory, but it works for many
users of the patch.

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