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

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Message-ID: <f32cffc4-c327-5019-3598-21516056b4e1@kernel.org>
Date:   Tue, 21 Mar 2023 16:38:59 +0200
From:   Georgi Djakov <djakov@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.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 21.03.23 16:11, Konrad Dybcio wrote:
> 
> 
> 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?

That's a good question. From what i recall, i expect them to persist until
you reset the board. Probably we can verify it with an experiment by reading
them back, but let me check if i can find some info.

Thanks,
Georgi