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

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Date:   Fri, 3 Mar 2023 12:39:23 +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
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 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