Message-ID: <0b1fafe6-0814-f1a6-ae19-7bd273751102@linaro.org>
Date:   Fri, 3 Mar 2023 12:42:40 +0100
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Subject: Re: [RFC PATCH] interconnect: qcom: icc-rpm: Don't call
 __qcom_icc_set twice on the same node
Content-Language: en-US
To:     Bryan O'Donoghue <bryan.odonoghue@linaro.org>,
        linux-arm-msm@vger.kernel.org, andersson@kernel.org,
        agross@kernel.org
Cc:     marijn.suijten@somainline.org, Georgi Djakov <djakov@kernel.org>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230303023500.2173137-1-konrad.dybcio@linaro.org>
 <59b28fb4-1367-9872-ed63-90847e380bb6@linaro.org>
 <29513b9e-8561-7f7e-370e-7515116c7ee6@linaro.org>
 <3116a08a-30a8-c9b9-f079-26739c9e6d49@linaro.org>
 <08020872-6316-8f81-ac6a-c6eef408818f@linaro.org>
 <db4f4e53-e8b9-0807-7490-2c6b76194ad5@linaro.org>
 <2cfba291-656f-9a43-fdd5-7601a6fe6ef5@linaro.org>
From:   Konrad Dybcio <konrad.dybcio@linaro.org>
In-Reply-To: <2cfba291-656f-9a43-fdd5-7601a6fe6ef5@linaro.org>
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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@linaro.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