linux-kernel - Re: [PATCH v3] dcdbas: Add support for WSMT ACPI table

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Date:   Mon, 2 Jul 2018 18:21:39 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Mario Limonciello <Mario.Limonciello@...l.com>
Cc:     Stuart Hayes <stuart.w.hayes@...il.com>,
        Darren Hart <dvhart@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>
Subject: Re: [PATCH v3] dcdbas: Add support for WSMT ACPI table

On Mon, Jul 2, 2018 at 5:07 PM,  <Mario.Limonciello@...l.com> wrote:

>> >> OK, now the most important question, did you investigate "SMM
>> >> Communication ACPI Table"?
>> >> Can you utilize information in it?
>>
>> > Dell BIOS does not provide a "SMM Communication ACPI Table", just the EPS.  It
>> appears
>> > that the "SMM Communication ACPI Table" is deprecated in the UEFI 2.7 spec.
>> Also, the
>> > dcdbas driver is for Dell systems only.
>>
>> > The EPS table isn't an ACPI table,
>> > it's just a Dell-defined table.
>>
>> Hmm... It's either strange or has some background why is so.
>> OK it has a note that there is no use case, but here it is!
>>
>> Mario, can we consider this as a BIOS bug which doesn't provide SMM
>> Communication ACPI table?
>>
>> Can it be escalated on UEFI committee?

> I don't believe SMM communication ACPI table has ever been implemented by Dell
> on server or client BIOS.  I do agree this table describes the behavior that DCDBAS driver
> has used since before even UEFI BIOS pretty accurately.

So, EPS table has been for ages in Dell machines?
Can we consider it as a predecessor of that SMM communication ACPI table?

> Stuart and I did discuss with server BIOS (who uses this EPS mechanism) to see if its possible
> to move EPS to SMM communication ACPI table however since it's been deprecated by
> UEFI 2.7 they weren't willing to adopt it.

It's pity, but the motivation to deprecate is "lack of use" which is
not true. That's why I would suggest to escalate this to UEFI
committee.

> Stuart, anything else you want to add here?

Darren, what's your opinion about this?

P.S. I'm not against this approach (just some technical comments I
already shared), but on the other hand it would be nice to have undo
that deprecation and follow the standard in new firmwares.
Would you agree?

-- 
With Best Regards,
Andy Shevchenko