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Date:   Tue, 4 Apr 2017 16:23:44 +0530
From:   George Cherian <>
To:     Hoan Tran <>,
        "Prakash, Prashanth" <>
Cc:     George Cherian <>,
        linux acpi <>,
        lkml <>,,
        Ashwin Chaugule <>,
        "Rafael J. Wysocki" <>,
        Len Brown <>,
        Jassi Brar <>,
        Robert Moore <>,
        Lv Zheng <>
Subject: Re: [PATCH 0/2] Make cppc acpi driver aware of pcc subspace ids

Hi Hoan/Prashanth,

On 04/03/2017 11:20 PM, Hoan Tran wrote:
> Hi George,
> On Mon, Apr 3, 2017 at 9:44 AM, Prakash, Prashanth
> <> wrote:
>> Hi George,
>> On 3/31/2017 12:24 AM, George Cherian wrote:
>>> The current cppc acpi driver works with only one pcc subspace id.
>>> It maintains and registers only one pcc channel even if the acpi table has
>>> different pcc subspace ids. The series tries to address the same by making
>>> cppc acpi driver aware of multiple possible pcc subspace ids.
>> The current ACPI 6.1 spec restricts the CPPC to a single PCC subspace. See section:
>> Using PCC Registers, which states "If the PCC register space is used, all PCC
>> registers must be defined to be in the same subspace."
> Agreed with Prashanth, beside of that, spec also says "To amortize the
> cost of PCC transactions, OSPM should read or
> write all PCC registers via a single read or write command when possible."

Yes indeed the spec says so but it was not at all a scalable solution 
when platform has more number of CPU's and CPU domains. That is why we 
took this approach.

> Thanks
> Hoan
>> --
>> Thanks,
>> Prashanth
>> --
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