linux-kernel - Re: [PATCH] ACPI/PPTT: use ACPI ID whenever ACPI_PPTT_ACPI_PROCESSOR_ID

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Date:   Mon, 2 Jul 2018 09:41:54 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Sudeep Holla <sudeep.holla@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        shunyong.yang@...-semitech.com, yu.zheng@...-semitech.com,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Jones <drjones@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH] ACPI/PPTT: use ACPI ID whenever
 ACPI_PPTT_ACPI_PROCESSOR_ID_VALID is set

Hi,

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@....com> 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 processor’s 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@...ysocki.net>
>>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>>> ---
>>>   drivers/acpi/pptt.c | 10 ++++++++--
>>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> Hi,
>>>
>>> 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.
>>
>> OK
>>
>> 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.