linux-kernel - Re: [PATCH v2 03/19] ARM: dts: Add DMC bus node for Exynos3250

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Message-id: <5668E0D6.7000200@samsung.com>
Date:	Thu, 10 Dec 2015 11:17:58 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	myungjoo.ham@...sung.com, kgene@...nel.org
Cc:	kyungmin.park@...sung.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux@....linux.org.uk,
	tjakobi@...h.uni-bielefeld.de, linux.amoon@...il.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 03/19] ARM: dts: Add DMC bus node for Exynos3250

On 2015년 12월 10일 11:04, Krzysztof Kozlowski wrote:
> On 10.12.2015 11:00, Chanwoo Choi wrote:
>> On 2015년 12월 10일 10:20, Krzysztof Kozlowski wrote:
>>> On 10.12.2015 10:09, Chanwoo Choi wrote:
>>>> On 2015년 12월 10일 09:44, Krzysztof Kozlowski wrote:
>>>>> On 09.12.2015 13:07, Chanwoo Choi wrote:
>>>>>> This patch adds the DMC (Dynamic Memory Controller) bus node for Exynos3250 SoC.
>>>>>> The DMC is an AMBA AXI-compliant slave to interface external JEDEC standard
>>>>>> SDRAM devices. The bus includes the OPP tables and the source clock for DMC
>>>>>> block.
>>>>>>
>>>>>> Following list specifies the detailed relation between the clock and DMC block:
>>>>>> - The source clock of DMC block : div_dmc
>>>>>>
>>>>>> Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
>>>>>> ---
>>>>>>  arch/arm/boot/dts/exynos3250.dtsi | 34 ++++++++++++++++++++++++++++++++++
>>>>>>  1 file changed, 34 insertions(+)
>>>>>>
>>>>>> diff --git a/arch/arm/boot/dts/exynos3250.dtsi b/arch/arm/boot/dts/exynos3250.dtsi
>>>>>> index 2f30d632f1cc..7214c5e42150 100644
>>>>>> --- a/arch/arm/boot/dts/exynos3250.dtsi
>>>>>> +++ b/arch/arm/boot/dts/exynos3250.dtsi
>>>>>> @@ -687,6 +687,40 @@
>>>>>>  			clock-names = "ppmu";
>>>>>>  			status = "disabled";
>>>>>>  		};
>>>>>> +
>>>>>> +		bus_dmc: bus_dmc {
>>>>>> +			compatible = "samsung,exynos-bus";
>>>>>> +			clocks = <&cmu_dmc CLK_DIV_DMC>;
>>>>>> +			clock-names = "bus";
>>>>>> +			operating-points-v2 = <&bus_dmc_opp_table>;
>>>>>> +			status = "disabled";
>>>>>> +		};
>>>>>> +
>>>>>> +		bus_dmc_opp_table: opp_table1 {
>>>>>
>>>>> This is the firsy opp_table, right? So:
>>>>> s/opp_table1/opp_table0/
>>>>
>>>> Right. It is first opp_table in exynos3250.dtsi.
>>>> But, I'm considering the OPP table of CPU freqeuncy as opp_table0.
>>>> So, I have the plan that support the operation-points-v2 for Exynos3250 CPU.
>>>
>>> Ok
>>>
>>>>
>>>>>
>>>>>> +			compatible = "operating-points-v2";
>>>>>> +			opp-shared;
>>>>>> +
>>>>>> +			opp00 {
>>>>>> +				opp-hz = /bits/ 64 <50000000>;
>>>>>> +				opp-microvolt = <800000>;
>>>>>> +			};
>>>>>> +			opp01 {
>>>>>> +				opp-hz = /bits/ 64 <100000000>;
>>>>>> +				opp-microvolt = <800000>;
>>>>>> +			};
>>>>>> +			opp02 {
>>>>>> +				opp-hz = /bits/ 64 <134000000>;
>>>>>> +				opp-microvolt = <800000>;
>>>>>
>>>>> Why 134, not 133 MHz?
>>>>
>>>> When I used the 133000000, the source clock is changed to 100Mhz instead of 133MHz.
>>>> I add following test result on exynos3250-rinato board.
>>>>
>>>> Case1.
>>>> When I use the 134 MHz, the source clock is changed to 133MHz
>>>> : exynos-bus soc:bus_dmc: old_freq(200000000) -> new_freq (134000000) (real: 133333334)
>>>>
>>>> Case2.
>>>> When I use the 133 MHz, the source clock is changed to 100MHz
>>>> : exynos-bus soc:bus_dmc: old_freq(200000000) -> new_freq (133000000) (real: 100000000)
>>>
>>> Now I remember that issue. You could use here directly 133333334 but
>>> that also would look a little bit weird... so 134 is ok for me. Could
>>> just add a comment that desired frequency is actually "133 MHz"?
>>
>> Do you prefer among following example?
>>
>> Example1.
>> 	opp02 {
>> 		/* The desired frequency is 133MHz because
>> 		 * clock change has the dependency on clock driver.
>> 		 * When set rate as 134MHz, the clock driver would
>> 		 * change the 133MHz actually instead of 134MHz.
>> 		 */
>> 		opp-hz = /bits/ 64 <134000000>;
>> 		opp-microvolt = <800000>;
>> 	};
>>
>> Example2.
>> 	opp02 {
>> 		opp-hz = /bits/ 64 <133333334>;
>> 		opp-microvolt = <800000>;
>> 	};
> 
> I would prefer the second one (133333334) but I don't have strong
> feelings about it.

If you ok, I want to maintain the original approach as following:

	opp02 {
		opp-hz = /bits/ 64 <134000000>;
		opp-microvolt = <800000>;
	};

Best Regards,
Chanwoo Choi

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