* Lin Ming <ming.m.lin@xxxxxxxxx>: > On Mon, 2009-12-21 at 03:30 +0800, Alex Chiang wrote: > > We discovered that at least one machine (HP Envy), methods in the DSDT > > attempt to call external methods defined in a dynamically loaded SSDT. > > > > Unfortunately, the DSDT methods we are trying to call are part of the > > EC initialization, which happens very early, and the the dynamic SSDT > > is only loaded when a processor _PDC method runs much later. > > > > This results in namespace lookup errors for the (as of yet) undefined > > methods. > > > > Since Windows doesn't have any issues with this machine, we take it > > as a hint that they must be evaluating _PDC much earlier than we are. > > > > Thus, the proper thing for Linux to do should be to match the Windows > > implementation more closely. > > > > Provide a mechanism to call _PDC before we enable the EC. Doing so loads > > the dynamic tables, and allows the EC to be enabled correctly. > > > > The ACPI processor driver will still evaluate _PDC in its .add() method > > to cover the hotplug case. > > > > Resolves: http://bugzilla.kernel.org/show_bug.cgi?id=14824 > > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c > > @@ -888,6 +888,8 @@ static int __init acpi_bus_init(void) > > goto error1; > > } > > > > + acpi_early_processor_set_pdc(); > > acpi_bus_init(...) { > acpi_ec_ecdt_probe(); > > acpi_initialize_objects(ACPI_FULL_INITIALIZATION); > > acpi_early_processor_set_pdc(); > > acpi_boot_ec_enable(); > } > > EC space handler may be installed in acpi_ec_ecdt_probe or > acpi_boot_ec_enable. In your machine(HP Envy), EC space > handler is installed in acpi_boot_ec_enable. Correct. > It seems that this patch does not fix the problem if EC space > hanlder is installed in acpi_ec_ecdt_probe, right? Also correct. But this patch is a reaction to reported behavior of a machine in the field, with a shipping BIOS, and the problem was that we only installed the handler in acpi_boot_ec_enable(). > But clearly, we can not put acpi_early_processor_set_pdc before > acpi_ec_ecdt_probe because ACPI namespace objects have not been > initialized yet at that time. > > Looks like a "chicken or the egg" problem. > Which came first, the chicken or the egg? I understand the point you are making, but in this case, we do know which came first (the chicken ;). Maybe in the future, we'll be surprised again and discover that we need to evaluate _PDC even earlier, but I prefer to fix that problem later, if it ever occurs, than to worry about it now. This patch fixes a real issue, so I prefer to focus on that instead of worrying about a theoretical issue. Thanks, /ac, unless Len tells me I'm wrong -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
