linux-kernel - Re: [PATCH RFC 1/2] ACPI/PPTT: Add acpi_pptt_get_package

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Date:   Tue, 28 Jan 2020 12:34:15 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     John Garry <john.garry@...wei.com>
Cc:     rjw@...ysocki.net, lenb@...nel.org, jeremy.linton@....com,
        arnd@...db.de, olof@...om.net, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, guohanjun@...wei.com,
        gregkh@...uxfoundation.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH RFC 1/2] ACPI/PPTT: Add acpi_pptt_get_package_info() API

On Tue, Jan 28, 2020 at 07:14:18PM +0800, John Garry wrote:
> The ACPI PPTT ID structure (see 6.2 spec, section 5.2.29.3) allows the
> vendor to provide an identifier (or vendor specific part number) for a
> particular processor hierarchy node structure. That may be a processor
> identifier for a processor node, or some chip identifier for a processor
> package node.
>

Unfortunately, there were plans to deprecate this in favour of the new
SOC_ID SMCCC API[1]. I am not sure if you or anyone in your company have
access to UEFI ASWG mantis where you can look for the ECR for the PPTT
Type 2 deprecation. I understand it's not ideal, but we need to converge,
please take a look at both before further discussion.

I personally would not prefer to add the support when I know it is getting
deprecated. I am not sure on kernel community policy on the same.


[...]

>
> The ID structure table has a number of fields, which are left open to
> interpretation per implementation. However the spec does provide reference
> examples of how the fields could be used. As such, just provide the
> table fields directly in the API, which the caller may interpret (probably
> as per spec example).
>

The "open for interpretation" part is why it's not being favoured anymore
by silicon vendors as OEM/ODMs can override the same.

> https://lore.kernel.org/linux-arm-kernel/1579876505-113251-6-git-send-email-john.garry@huawei.com/
>
Ah, there's already quite a lot of dependency built for this feature :(

--
Regards,
Sudeep

[1] https://developer.arm.com/docs/den0028/c