linux-kernel - Re: [RFC PATCH] interconnect: qcom: icc-rpm: Don't call __qcom_icc

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Date:   Fri, 3 Mar 2023 11:50:15 +0000
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, andersson@...nel.org,
        agross@...nel.org
Cc:     marijn.suijten@...ainline.org, Georgi Djakov <djakov@...nel.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] interconnect: qcom: icc-rpm: Don't call
 __qcom_icc_set twice on the same node

On 03/03/2023 11:42, Konrad Dybcio wrote:
> 
> 
> On 3.03.2023 12:40, Bryan O'Donoghue wrote:
>> On 03/03/2023 11:39, Konrad Dybcio wrote:
>>>
>>>
>>> On 3.03.2023 12:36, Bryan O'Donoghue wrote:
>>>> On 03/03/2023 11:35, Bryan O'Donoghue wrote:
>>>>> On 03/03/2023 11:33, Konrad Dybcio wrote:
>>>>>>
>>>>>>
>>>>>> On 3.03.2023 12:32, Bryan O'Donoghue wrote:
>>>>>>> On 03/03/2023 02:35, Konrad Dybcio wrote:
>>>>>>>> Currently, when sync_state calls set(n, n) all the paths for setting
>>>>>>>> parameters on an icc node are called twice. Avoid that.
>>>>>>>>
>>>>>>>> Fixes: 751f4d14cdb4 ("interconnect: icc-rpm: Set destination bandwidth as well as source bandwidth")
>>>>>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>>>>>>> ---
>>>>>>>> RFC comes from the fact that I *believe* this should be correct, but I'm
>>>>>>>> not entirely sure about it..
>>>>>>>>
>>>>>>>>
>>>>>>>>      drivers/interconnect/qcom/icc-rpm.c | 2 +-
>>>>>>>>      1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/interconnect/qcom/icc-rpm.c b/drivers/interconnect/qcom/icc-rpm.c
>>>>>>>> index a6e0de03f46b..d35db1af9b08 100644
>>>>>>>> --- a/drivers/interconnect/qcom/icc-rpm.c
>>>>>>>> +++ b/drivers/interconnect/qcom/icc-rpm.c
>>>>>>>> @@ -387,7 +387,7 @@ static int qcom_icc_set(struct icc_node *src, struct icc_node *dst)
>>>>>>>>          ret = __qcom_icc_set(src, src_qn, sum_bw);
>>>>>>>>          if (ret)
>>>>>>>>              return ret;
>>>>>>>> -    if (dst_qn) {
>>>>>>>> +    if (dst_qn && src_qn != dst_qn) {
>>>>>>>>              ret = __qcom_icc_set(dst, dst_qn, sum_bw);
>>>>>>>>              if (ret)
>>>>>>>>                  return ret;
>>>>>>>
>>>>>>> Is it possible for src_qn == dst_qn ?
>>>>>> As the commit message says, sync_state calls set(n, n) in
>>>>>> drivers/interconnect/core.c : icc_sync_state(struct device *dev)
>>>>>
>>>>> So you've _seen_ that happen ?
>>>>>
>>>>
>>>> Assuming you have, then why isn't the fix in sync_state i.e. that's an error for everybody right ?
>>> I believe that there's simply no other way of updating every single node
>>> on its own with the icc api, without taking any links into play. But I
>>> see exynos and i.mx also effectively calling it twice on each node.
>>>
>>> Konrad
>>
>> I mean. I'm fine for you to retain my RB on this qcom specific patch since this seems like a real bug to me but... it seems like a generic bug across arches that should probably be resolved @ the higher level.
>>
>> ?
> I suppose we could change the set(n, n) in sync_state to be set(n, NULL)
> and enforce parameter null-checking on all provider->set functions. Do
> I understand this correctly?
> 
> Konrad
>>
>> ---
>> bod

void icc_sync_state(struct device *dev)
{
         struct icc_provider *p;
         struct icc_node *n;
         static int count;

         count++;

         if (count < providers_count)
                 return;

         mutex_lock(&icc_lock);
         synced_state = true;
         list_for_each_entry(p, &icc_providers, provider_list) {
                 dev_dbg(p->dev, "interconnect provider is in synced 
state\n");
                 list_for_each_entry(n, &p->nodes, node_list) {
                         if (n->init_avg || n->init_peak) {
                                 n->init_avg = 0;
                                 n->init_peak = 0;
                                 aggregate_requests(n);
                                 p->set(n, n);
                         }
                 }
         }
         mutex_unlock(&icc_lock);
}
EXPORT_SYMBOL_GPL(icc_sync_state);

I mean p->set(n,n); is done like this since forever. Now that you draw 
attention to it, it doesn't make much sense to me..