linux-kernel - Re: [PATCH v7 6/9] interconnect: qcom: rpm: Handle interface clocks

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Message-ID: <5459d8d3-4829-01ab-7000-2c1f58ad69e8@linaro.org>
Date:   Tue, 21 Mar 2023 15:11:25 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Georgi Djakov <djakov@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 6/9] interconnect: qcom: rpm: Handle interface clocks



On 21.03.2023 14:58, Georgi Djakov wrote:
> Hi,
> 
> On 11.03.23 17:26, Dmitry Baryshkov wrote:
>> On 11/03/2023 16:38, Bryan O'Donoghue wrote:
>>> On 11/03/2023 14:35, Dmitry Baryshkov wrote:
>>>>> Its probably worthwhile experimenting to see if the*ufs*_clk can/should
>>>>> be added to the UFS device list of clocks.
>>>> While we were doing this for some of the clocks (PCIe and USB, if I'm
>>>> not mistaken), I think that generally this is not fully correct. In my
>>>> opinion it should be in the interconnect driver, who turns
>>>> corresponding clocks on and off. These clocks correspond to the SoC
>>>> topology, rather than the end-device.
>>>>
>>>
>>> True enough, they are interconnect clocks.
>>>
>>> The question is how to only turn them on when the device that depends on them wants them.
>>
>> I think we can turn them on an off from qcom_icc_set(). Each node can list required clocks.
>>
> 
> Yes, this is a bit weird, but looks like these are the interface clocks
> required for programming the qos box of the respective peripheral and
> nothing else. Maybe we can even configure QoS just once (eg. on the first
> bandwidth request) and not every time we call qcom_icc_set().
Would that persist a full bus reset - if we e.g. shut down MMNoC 
after the display stack is turned off in preparation for a power
collapse, would we have to reprogram it?

Another thing is, do we know "how persistent" the QoS settings are?
What could reset them? Would a bandwidth request for a node that
belongs to the same path do so?

Konrad
> 
> BR,
> Georgi