From: Jeremy Linton
Date: Mon Jul 02 2018 - 10:42:00 EST


On 07/02/2018 04:57 AM, Sudeep Holla wrote:

On 02/07/18 10:06, Rafael J. Wysocki wrote:
On Fri, Jun 29, 2018 at 6:17 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
Currently we use the ACPI processor ID only for the leaf/processor nodes
as the specification states it must match the value of ACPI processor ID
field in the processorâs entry in the MADT.

However, if a PPTT structure represents processors group, it match a
processor container UID in the namespace and ACPI_PPTT_ACPI_PROCESSOR_ID_VALID
flag describe whether the ACPI processor ID is valid.

Lets use UID whenever ACPI_PPTT_ACPI_PROCESSOR_ID_VALID is set to be
consistent instead of using table offset as it's currently done for non
leaf nodes.

Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
drivers/acpi/pptt.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)


There's ongoing discussion on assigning ID based in OS using simple
counters. It can never be consistent with firmware's view. So if the
firmware provides valid UID for non-processors node, we must use it.


Do you regard this as a fix for the recently merged PPTT material? If
so, I should apply it as a fix for 4.18.

Yes, it should be considered as fix IMO.

Do we know which machines are affected?

I'm mostly agnostic to this patch because I believe its effectively a NOP. But that said, it could have a functional change, which implies there is some risk.