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Subject: Re: [RFC RESEND PATCH 0/7] Add driver for dvfsrc and add support for
 active state of scpsys on mt8183
To:     Henry Chen <henryc.chen@mediatek.com>
Cc:     Stephen Boyd <swboyd@chromium.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Viresh Kumar <vireshk@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Fan Chen <fan.chen@mediatek.com>,
        Weiyi Lu <weiyi.lu@mediatek.com>,
        James Liao <jamesjj.liao@mediatek.com>,
        Kees Cook <keescook@chromium.org>, linux-pm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
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From:   Georgi Djakov <georgi.djakov@linaro.org>
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Message-ID: <d03ec933-5fe6-d076-d658-9b966cee9c0f@linaro.org>
Date:   Thu, 10 Jan 2019 11:39:03 +0200
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On 1/9/19 05:08, Henry Chen wrote:
> On Mon, 2019-01-07 at 18:34 +0200, Georgi Djakov wrote:
>> Hi Henry,
>>
>> On 1/7/19 13:04, Henry Chen wrote:
>>> On Thu, 2019-01-03 at 14:53 -0800, Stephen Boyd wrote:
>>>> Quoting Henry Chen (2019-01-02 06:09:51)
>>>>> The patchsets add support for MediaTek hardware module named DVFSRC
>>>>> (dynamic voltage and frequency scaling resource collector). The DVFSRC is
>>>>> a HW module which is used to collect all the requests from both software
>>>>> and hardware and turn into the decision of minimum operating voltage and
>>>>> minimum DRAM frequency to fulfill those requests.
>>>>>
>>>>> So, This series is to implement the dvfsrc driver to collect all the
>>>>> requests of operating voltage or DRAM bandwidth from other device drivers
>>>>> likes GPU/Camera through 2 frameworks basically:
>>>>>
>>>>> 1. PM_QOS_MEMORY_BANDWIDTH from PM QOS: to aggregate the bandwidth
>>>>>    requirements from different clients
>>>>
>>>> Have you looked at using the interconnect framework for this instead of
>>>> using PM_QOS_MEMORY_BANDWIDTH? Qcom is pushing an interconnect framework
>>>> to do DRAM bandwidth requirement aggregation.
>>>
>>> Sorry, I haven't heard that before. Do you mean is following series
>>> patch?
>>> https://patchwork.kernel.org/project/linux-arm-msm/list/?series=53775
>>>
>>
>> Yes, this one. The idea is that consumer drivers like GPU, camera, video
>> encoder etc. report their bandwidth needs by using the interconnect API.
>> The framework does the aggregation and configures the hardware. In order
>> to use it you need to implement a platform-specific dvfsrc interconnect
>> provider driver that understands the SoC topology and knows how to
>> configure the hardware. I am not familiar with DVFSRC, but it seems to
>> me that it can fit as interconnect provider.
>> Does this HW module support any QoS priority/latency configuration or is
>> it only bandwidth and voltage?
>>
>> Thanks,
>> Georgi
> 
> Hi Georgi,
> 
> Yes, the design is only to support bandwidth and voltage. The one of the
> function is to collect the memory bandwidth requirement from consumer
> and select the minimum DRAM frequency to fulfill system performance.It
> just get the total bandwidth then set it to HW, not involves complex SoC
> topology. So we choose to use PM QOS to model that DVFSRC driver can
> receive the bandwidth information from consumer driver via
> PM_QOS_MEMORY_BANDWIDTH.

Ok, good. The current patchset supports bandwidth, but there was a
discussion about adding support for latency and priority in the future.
Thanks for the information!

> Do you have a patch that show how consumer driver used interconnect to
> update their requirement.

Here are some examples:
https://lkml.org/lkml/2018/12/7/584
https://lkml.org/lkml/2018/10/11/499
https://lkml.org/lkml/2018/9/20/986
https://lkml.org/lkml/2018/11/22/772

Thanks,
Georgi