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

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Message-ID: <ad231bd5-4308-4a69-86c5-5431eba2807d@linaro.org>
Date:   Sat, 18 Feb 2023 00:19:34 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...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 22:28, Konrad Dybcio wrote:
> 
> 
> 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.

Would 'lesser ugliness' count? Maybe add a define 'ICC_RPM_NO_CLOCKS = 
-1'? I think that spawning default bus & bus_a everywhere would be worse.

When this driver is rewritten in Rust, we'll have a clear distinction 
between None (meaning default two clocks) and Some(0) (meaning no 
clocks). Wait, does that sound even more ugly?

-- 
With best wishes
Dmitry