linux-kernel - Re: [PATCH v5 08/10] interconnect: qcom: msm8996: Specify no bus clock scaling on A0NoC

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Date:   Fri, 17 Feb 2023 21:28:54 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Jun Nie <jun.nie@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Brian Masney <masneyb@...tation.org>,
        Yassine Oudjana <y.oudjana@...tonmail.com>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 08/10] interconnect: qcom: msm8996: Specify no bus
 clock scaling on A0NoC



On 17.02.2023 21:26, Dmitry Baryshkov wrote:
> On Fri, 17 Feb 2023 at 21:53, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>>
>>
>>
>> On 17.02.2023 20:27, Konrad Dybcio wrote:
>>>
>>>
>>> On 17.02.2023 11:46, Konrad Dybcio wrote:
>>>> A0NoC only does bus scaling through RPM votes and does not have any
>>>> ICC clocks. Describe this.
>>>>
>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>>> ---
>>> This is bad, as devm_clk_get_bulk{"", _optional} doesn't
>>> check if num_clocks makes sense and passes "-1" down the
>>> devres alloc chain..
>>>
>>> I'll rework this for the next revision by simply assigning
>>> the common "bus", "bus_a" set everywhere instead of relying
>>> on it being there by default..
>> Or maybe I shouldn't, as that will require redefining the array
>> over and over again.. Perhaps just passing <&xo_board>, <&xo_board>
>> to a0noc's "bus", "bus_a", similar to what's been done on SDM630's
>> GNoC would be less messy?
> 
> What about simply skipping a call to devm_clk_get if num_bus_clocks is negative?
I tested that locally before reporting the mistake on my side and
while it works, I just consider it.. ugly, because:

num_clocks =
>0 => use the externally specified num_/clocks (logical)
=0 => use the default 2
<0 => consider there's zero

..but maybe that's just me.. if you don't find it ugly, I may just
go with that.

Konrad
> 
>>
>> Konrad
>>>
>>> Konrad
>>>>  drivers/interconnect/qcom/msm8996.c | 1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/interconnect/qcom/msm8996.c b/drivers/interconnect/qcom/msm8996.c
>>>> index 1a5e0ad36cc4..45eb8675fb11 100644
>>>> --- a/drivers/interconnect/qcom/msm8996.c
>>>> +++ b/drivers/interconnect/qcom/msm8996.c
>>>> @@ -1817,6 +1817,7 @@ static const struct qcom_icc_desc msm8996_a0noc = {
>>>>      .type = QCOM_ICC_NOC,
>>>>      .nodes = a0noc_nodes,
>>>>      .num_nodes = ARRAY_SIZE(a0noc_nodes),
>>>> +    .num_bus_clocks = -1, /* No bus clock scaling */
>>>>      .intf_clocks = a0noc_intf_clocks,
>>>>      .num_intf_clocks = ARRAY_SIZE(a0noc_intf_clocks),
>>>>      .has_bus_pd = true,
>>>>
> 
> 
>