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

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Date:   Tue, 21 Mar 2023 15:23:02 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Georgi Djakov <djakov@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Bryan O'Donoghue <bryan.odonoghue@...aro.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 14:56, Georgi Djakov wrote:
> Hi Konrad,
> 
> Thank you for working on this and sorry about jumping a bit late into
> the discussion.
> 
> On 8.03.23 23:40, Konrad Dybcio wrote:
>> Some (but not all) providers (or their specific nodes) require
>> specific clocks to be turned on before they can be accessed. Failure
>> to ensure that results in a seemingly random system crash (which
>> would usually happen at boot with the interconnect driver built-in),
>> resulting in the platform not booting up properly.
> 
> These "interface" clocks seem to be used only to program QoS for the
> respective ip block (eg ufs). So if we don't program QoS, there should
> be no crashes, right?
Correct.

> 
> I believe that in downstream they defer setting QoS until the first
> non-zero bandwidth request because of drivers that probe asynchronously
> or there is some firmware booting involved (IPA maybe). 
Hmm.. that would make sense.

> And bad stuff
> might happen if we touch the clock while the firmware is still booting.
> So setting the QoS on the first non-zero bandwidth request might not be
> a bad idea.
Sounds like a plan, I don't think setting QoS parameters on buses
that are not in use does anything (citation needed).

Such nodes should probably be also excluded from sync_state
> by implementing get_bw() to return 0 bandwidth.
I agree, setting the QoS parameters in sync_state (so, without
their dependencies fully met) sounds like a recipe for disaster,
while getting rid of QoS in sync_state at all would leave the nodes
that are not explicitly referenced in the device tree unconfigured.


Konrad

> 
> BR,
> Georgi
> 
>>
>> Limit the number of bus_clocks to 2 (which is the maximum that SMD
>> RPM interconnect supports anyway) and handle non-scaling clocks
>> separately. Update MSM8996 and SDM660 drivers to make sure they do
>> not regress with this change.
>>
>> This unfortunately has to be done in one patch to prevent either
>> compile errors or broken bisect.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>> ---
>>   drivers/interconnect/qcom/icc-rpm.c | 52 ++++++++++++++++++++++++++++++-------
>>   drivers/interconnect/qcom/icc-rpm.h | 14 ++++++++--
>>   drivers/interconnect/qcom/msm8996.c | 22 +++++++---------
>>   drivers/interconnect/qcom/sdm660.c  | 16 +++++-------
>>   4 files changed, 70 insertions(+), 34 deletions(-)
>>
> [..]
>