linux-kernel - Re: [PATCH 1/4] interconnect: qcom: rpm: Don't set QoS params before non-zero bw is requested

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Date:   Wed, 4 Jan 2023 01:25:17 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        linux-arm-msm@...r.kernel.org, andersson@...nel.org,
        agross@...nel.org, krzysztof.kozlowski@...aro.org
Cc:     marijn.suijten@...ainline.org, Georgi Djakov <djakov@...nel.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] interconnect: qcom: rpm: Don't set QoS params before
 non-zero bw is requested



On 4.01.2023 00:07, Bryan O'Donoghue wrote:
> On 03/01/2023 17:30, Konrad Dybcio wrote:
>> Until now, the icc-rpm driver unconditionally set QoS params, even on
>> empty requests. This is superfluous and the downstream counterpart does
>> not do it. Follow it by doing the same.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>> ---
>>   drivers/interconnect/qcom/icc-rpm.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/interconnect/qcom/icc-rpm.c b/drivers/interconnect/qcom/icc-rpm.c
>> index 43b9ce0dcb6a..06e0fee547ab 100644
>> --- a/drivers/interconnect/qcom/icc-rpm.c
>> +++ b/drivers/interconnect/qcom/icc-rpm.c
>> @@ -193,6 +193,12 @@ static int qcom_icc_qos_set(struct icc_node *node, u64 sum_bw)
>>       struct qcom_icc_provider *qp = to_qcom_provider(node->provider);
>>       struct qcom_icc_node *qn = node->data;
>>   +    /* Defer setting QoS until the first non-zero bandwidth request. */
>> +    if (!(node->avg_bw || node->peak_bw)) {
>> +        dev_dbg(node->provider->dev, "NOT Setting QoS for %s\n", qn->name);
>> +        return 0;
>> +    }
>> +
>>       dev_dbg(node->provider->dev, "Setting QoS for %s\n", qn->name);
>>         switch (qp->type) {
> 
> Doesn't downstream clear the registers on a zero allocation request ?
> 
> https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.BR.1.2.9-00810-8x09.0/drivers/platform/msm/msm_bus/msm_bus_bimc.c#L1302
> 
> https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.BR.1.2.9-00810-8x09.0/drivers/platform/msm/msm_bus/msm_bus_bimc.c#L1318
> 
> https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.BR.1.2.9-00810-8x09.0/drivers/platform/msm/msm_bus/msm_bus_bimc.c#L1367
> 
> msm_bus_bimc_set_qos_bw()
> {
>     /* Only calculate if there's a requested bandwidth and window */
>     if (qbw->bw && qbw->ws) {
>     }else
>         /* Clear bandwidth registers */
>         set_qos_bw_regs(base, mas_index, 0, 0, 0, 0, 0);
> }
Yes, looks like that's the case, but also it's only for BIMC, not
for NOC:

https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.BR.1.2.9-00810-8x09.0/drivers/platform/msm/msm_bus/msm_bus_noc.c#L246

Moreover, it only concerns QoS parameters that are not supported on
mainline (Grant Period, Grant Count, Threshold Lo/Me/Hi) [1], so that
pretty much addresses your worries, I think..

And FWIW that's definitely not the case anymore for QNOC (and BIMC
for that matter) on msm-5.4:

https://github.com/sonyxperiadev/kernel/blob/aosp/LA.UM.9.14.r1/drivers/interconnect/qcom/icc-rpm.c#L217


Konrad

[1] Note: msm8939 seems to be a somewhat heavy user of these properties,
maybe it would be worth looking into implementing them?
> 
> ---
> bod