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

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Message-id: <5668E199.7010001@samsung.com>
Date:	Thu, 10 Dec 2015 11:21:13 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Chanwoo Choi <cw00.choi@...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 10.12.2015 11:17, Chanwoo Choi wrote:
> 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>;
> 	};

OK

Best regards,
Krzysztof

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