linux-kernel - Re: [PATCH v2] arm64: dts: ti: k3-j721e: Add support for DFS in J721E A72

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Date: Fri, 5 Jan 2024 09:26:45 +0530
From: Neha Malcom Francis <n-francis@...com>
To: Nishanth Menon <nm@...com>
CC: <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <vigneshr@...com>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <a-nandan@...com>, <kristo@...nel.org>, <u-kumar1@...com>
Subject: Re: [PATCH v2] arm64: dts: ti: k3-j721e: Add support for DFS in J721E
 A72

Hi Nishanth,

On 04/01/24 20:46, Nishanth Menon wrote:
> On 16:49-20240104, Neha Malcom Francis wrote:
>> Add 2G, 1G, 500M and 250M as the supported frequencies for A72. This
>> enables support for Dynamic Frequency Scaling (DFS). Note that Dynamic
>> Voltage and Frequency Scaling (DVFS) is not supported on J7 devices.
>>
>> J721E SoC has three different speed grade devices (see [1], 7.5
>> Operating Performance Points) which as of today are indiscernible in
>> software, users of a different speed grade device must manually change
>> the DTS to ensure their maximum speed frequency is supported.
>>
>> To obtain clock-latency-ns, the maximum time was found to switch from/to
>> any frequency for a CPU and this value was rounded off and set.
>>
>> [1] https://www.ti.com/lit/gpn/tda4vm
>>
>> Signed-off-by: Neha Malcom Francis <n-francis@...com>
>> ---
>> Test and boot logs:
>> https://gist.github.com/nehamalcom/33608837ab5ad3332ff11a7fa7a602e2
>>
>> Changes since v1:
>> https://lore.kernel.org/all/20231214075637.176586-1-n-francis@ti.com/
>> - removed OPPs 1.5G and 750M as they introduced boot regression in
>>    J721E-SK
> 
> I do not think this is the right approach precisely for the above
> reason.
> 
> See my comment in V1: https://lore.kernel.org/all/20231214125130.zqtq6ioj4c533wha@elbow/
> 
> "
> I am also concerned if the table should be separated out as a dtsi and
> included at board.dts level to prevent downstream users going crazy..
> "
> 
> I suspect there is no magic opp configuration that will work with all
> downstream and board variations. instead of creating a trimmed down
> non-datasheet tuples of OPP configuration, use the data sheet provided
> OPP configurations into each dtsi and the boards can apply the dtsi
> based on the type of sample they have.
> 
> I don't see any other scheme (overlays, maybe?).. but this approach is
> broken and your note above proves why this approach is broken.
> 

Understood... I believed OPPs were an SoC specific thing until this failure came 
about and it makes sense to take it at the board level now. Will factor this in 
for v3.

>> - Nishanth
>> 	- indicated DVFS not supported in commit message
>> 	- moved critical data sheet info from below tear line to commit
>> 	  message
>> 	- added opp-shared property
>> 	- added clock-latency-ns property
>>
>>   arch/arm64/boot/dts/ti/k3-j721e.dtsi | 31 ++++++++++++++++++++++++++++
>>   1 file changed, 31 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/ti/k3-j721e.dtsi b/arch/arm64/boot/dts/ti/k3-j721e.dtsi
>> index a200810df54a..5de6c70bd989 100644
>> --- a/arch/arm64/boot/dts/ti/k3-j721e.dtsi
>> +++ b/arch/arm64/boot/dts/ti/k3-j721e.dtsi
>> @@ -48,6 +48,9 @@ cpu0: cpu@0 {
>>   			d-cache-line-size = <64>;
>>   			d-cache-sets = <256>;
>>   			next-level-cache = <&L2_0>;
>> +			clocks = <&k3_clks 202 2>;
>> +			clock-names = "cpu";
>> +			operating-points-v2 = <&cpu0_opp_table>;
>>   		};
>>   
>>   		cpu1: cpu@1 {
>> @@ -62,6 +65,34 @@ cpu1: cpu@1 {
>>   			d-cache-line-size = <64>;
>>   			d-cache-sets = <256>;
>>   			next-level-cache = <&L2_0>;
>> +			clocks = <&k3_clks 203 0>;
>> +			clock-names = "cpu";
>> +			operating-points-v2 = <&cpu0_opp_table>;
>> +		};
>> +	};
>> +
>> +	cpu0_opp_table: opp-table {
>> +		compatible = "operating-points-v2";
>> +		opp-shared;
>> +
>> +		opp6-2000000000 {
>> +			opp-hz = /bits/ 64 <2000000000>;
>> +			clock-latency-ns = <300000>;
>> +		};
>> +
>> +		opp4-1000000000 {
>> +			opp-hz = /bits/ 64 <1000000000>;
>> +			clock-latency-ns = <300000>;
>> +		};
>> +
>> +		opp2-500000000 {
>> +			opp-hz = /bits/ 64 <500000000>;
>> +			clock-latency-ns = <300000>;
>> +		};
>> +
>> +		opp1-250000000 {
>> +			opp-hz = /bits/ 64 <250000000>;
>> +			clock-latency-ns = <300000>;
>>   		};
>>   	};
>>   
>> -- 
>> 2.34.1
>>
> 

-- 
Thanking You
Neha Malcom Francis