Subject: Re: [PATCH 0/2] Make cppc acpi driver aware of pcc subspace ids
To: Hoan Tran <hotran@apm.com>,
        "Prakash, Prashanth" <pprakash@codeaurora.org>
References: <1490941442-11954-1-git-send-email-george.cherian@cavium.com>
 <ccc72eec-4a43-b976-0195-49a7c0029641@codeaurora.org>
 <CAFHUOYzf_CFcYCCTbgpJ_Orp_fJMLX8DD=ag-f3TBv0FeY-CRA@mail.gmail.com>
Cc: George Cherian <george.cherian@cavium.com>,
        linux acpi <linux-acpi@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, devel@acpica.org,
        Ashwin Chaugule <ashwin.chaugule@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, Len Brown <lenb@kernel.org>,
        Jassi Brar <jassisinghbrar@gmail.com>,
        Robert Moore <robert.moore@intel.com>, Lv Zheng <lv.zheng@intel.com>
From: George Cherian <gcherian@caviumnetworks.com>
Message-ID: <58E37B38.2030204@caviumnetworks.com>
Date: Tue, 4 Apr 2017 16:23:44 +0530
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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
> <pprakash@codeaurora.org> 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:
>> 8.4.7.1.9 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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