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SubjectRe: [PATCH] interconnect: Skip call into provider if initial bw is zero
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Hi Bryan,
Thanks for taking time to review the patch.

On 1/13/2023 5:40 PM, Bryan O'Donoghue wrote:
> On 14/01/2023 01:24, Bryan O'Donoghue wrote:
>> On 13/01/2023 22:07, Vivek Aknurwar wrote:
>>> Currently framework sets bw even when init bw requirements are zero
>>> during
>>> provider registration, thus resulting bulk of set bw to hw.
>>> Avoid this behaviour by skipping provider set bw calls if init bw is
>>> zero.
>>>
>>> Signed-off-by: Vivek Aknurwar <quic_viveka@quicinc.com>
>>> ---
>>>   drivers/interconnect/core.c | 17 ++++++++++-------
>>>   1 file changed, 10 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
>>> index 25debde..43ed595 100644
>>> --- a/drivers/interconnect/core.c
>>> +++ b/drivers/interconnect/core.c
>>> @@ -977,14 +977,17 @@ void icc_node_add(struct icc_node *node, struct
>>> icc_provider *provider)
>>>       node->avg_bw = node->init_avg;
>>>       node->peak_bw = node->init_peak;
>>> -    if (provider->pre_aggregate)
>>> -        provider->pre_aggregate(node);
>>> -
>>> -    if (provider->aggregate)
>>> -        provider->aggregate(node, 0, node->init_avg, node->init_peak,
>>> -                    &node->avg_bw, &node->peak_bw);
>>> +    if (node->avg_bw || node->peak_bw) {
>>> +        if (provider->pre_aggregate)
>>> +            provider->pre_aggregate(node);
>>> +
>>> +        if (provider->aggregate)
>>> +            provider->aggregate(node, 0, node->init_avg,
>>> node->init_peak,
>>> +                        &node->avg_bw, &node->peak_bw);
>>> +        if (provider->set)
>>> +            provider->set(node, node);
>>> +    }
>>> -    provider->set(node, node);
>>>       node->avg_bw = 0;
>>>       node->peak_bw = 0;
>>
>> I have the same comment/question for this patch that I had for the
>> qcom arch specific version of it. This patch seems to be doing at a
>> higher level what the patch below was doing at a lower level.
>>
>> https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@linaro.org/T/#m0c90588d0d1e2ab88c39be8f5f3a8f0b61396349
>>
>> what happens to earlier silicon - qcom silicon which previously made
>> explicit zero requests ?

This patch is to optimize and avoid all those bw 0 requests on each node
addition during probe (which results in rpmh remote calls) for upcoming
targets.

>>
>> https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@linaro.org/T/#m589e8280de470e038249bb362634221771d845dd
>>
>> https://lkml.org/lkml/2023/1/3/1232
>>
>> Isn't it a better idea to let lower layer drivers differentiate what
>> they do ?

AFAIU lower layer driver can/should not differentiate between normal
flow calls vs made as a result from probe/initialization of driver.
Hence even bw 0 request is honored as like client in general wish to
vote 0 as in an normal use case.

>>
>> For example on pre 5.4 qcom kernel silicon we might choose to set the
>> value to zero "because that's what the reference code did" but on
>> newer silicon we might opt to skip the zero configuration ?
>>
>> I'm happy to be shown the error of my ways but, absent testing to
>> *show* it doesn't impact existing legacy silicon, I think we should be
>> wary of this change.
>>
>> ---
>> bod
>
> Oh, and what is the effect on Samsung and i.MX silicon interconnect
> providers of skipping the zero set ?

If interconnect providers are trying to clear bw votes coming from
boot-loader then best place to clear those is in sync-state call back.

>
> ---
> bod

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