linux-kernel - Re: [PATCH v3 03/17] arm64: dts: sdm845: Add OPP table for all qup devices

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Date:   Wed, 29 Apr 2020 22:08:15 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     viresh.kumar@...aro.org, sboyd@...nel.org,
        bjorn.andersson@...aro.org, agross@...nel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v3 03/17] arm64: dts: sdm845: Add OPP table for all qup
 devices


On 4/29/2020 9:40 PM, Matthias Kaehlcke wrote:
> On Wed, Apr 29, 2020 at 08:23:30PM +0530, Rajendra Nayak wrote:
>>
>> On 4/29/2020 7:45 PM, Rajendra Nayak wrote:
>>>
>>> On 4/29/2020 5:32 AM, Matthias Kaehlcke wrote:
>>>> Hi Rajendra,
>>>>
>>>> On Tue, Apr 28, 2020 at 07:02:51PM +0530, Rajendra Nayak wrote:
>>>>> qup has a requirement to vote on the performance state of the CX domain
>>>>> in sdm845 devices. Add OPP tables for these and also add power-domains
>>>>> property for all qup instances.
>>>>>
>>>>> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
>>>>> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
>>>>> ---
>>>>>    arch/arm64/boot/dts/qcom/sdm845.dtsi | 115 +++++++++++++++++++++++++++++++++++
>>>>>    1 file changed, 115 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm64/boot/dts/qcom/sdm845.dtsi b/arch/arm64/boot/dts/qcom/sdm845.dtsi
>>>>> index 8f926b5..36b9fb1 100644
>>>>> --- a/arch/arm64/boot/dts/qcom/sdm845.dtsi
>>>>> +++ b/arch/arm64/boot/dts/qcom/sdm845.dtsi
>>>>> @@ -804,6 +804,25 @@
>>>>>                clock-names = "core";
>>>>>            };
>>>>> +        qup_opp_table: qup-opp-table {
>>>>> +            compatible = "operating-points-v2";
>>>>> +
>>>>> +            opp-19200000 {
>>>>> +                opp-hz = /bits/ 64 <19200000>;
>>>>> +                required-opps = <&rpmhpd_opp_min_svs>;
>>>>> +            };
>>>>> +
>>>>> +            opp-75000000 {
>>>>> +                opp-hz = /bits/ 64 <75000000>;
>>>>> +                required-opps = <&rpmhpd_opp_low_svs>;
>>>>> +            };
>>>>> +
>>>>> +            opp-100000000 {
>>>>> +                opp-hz = /bits/ 64 <100000000>;
>>>>> +                required-opps = <&rpmhpd_opp_svs>;
>>>>> +            };
>>>>> +        };
>>>>> +
>>>>
>>>> Judging from SDM845 (which has more OPP tables) the convention seems to be
>>>> to add OPP tables to the nodes that use them, which seems reasonable and
>>>> keeps them out of the device list.
>>>>
>>>> Unfortunately this convention isn't completely suitable for cases like this
>>>> (and the DSI OPPs later in this series), where the same OPP table is used by
>>>> multiple devices. A possible compromise would be to add the table to the
>>>> node of the first device that uses them.
>>>
>>> Sounds fair, I will do that and respin. Thanks.
>>
>> Looking into this some more, I see we do have..
>>
>> static const struct of_device_id of_skipped_node_table[] = {
>>          { .compatible = "operating-points-v2", },
>>          {} /* Empty terminated list */
>> };
>>
>> ..in drivers/of/platform.c, so its not being added to the device list.
> 
> sure, I didn't mean that the OPP table is added by the kernel as a device, but
> that the table breaks with the structure of the DT of device nodes ordered by
> address.

Ah ok, got it.

> 
>> And atleast in case of qup, I am having to duplicate the OPP tables once for
>> each qup instance. Not to mention, having them inside the first qup device
>> just makes it a little confusing to read who the OPP table belongs to.
> 
> I'm not advocating for duplicating the OPP tables. An alternative to having
> them in the first QUP device could be to have an dedicated node with shared
> opp tables outside of the device list, similar to thermal-zones.

That sounds like a good idea too.

> I tend to like consistency and the sprinkled in OPP tables break with that,
> but ultimately it's up to Bjorn.

Bjorn, any thoughts?

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