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:

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On 2015년 12월 10일 10:20, Krzysztof Kozlowski wrote:

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On 10.12.2015 10:09, Chanwoo Choi wrote:

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On 2015년 12월 10일 09:44, Krzysztof Kozlowski wrote:

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On 09.12.2015 13:07, Chanwoo Choi wrote:

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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@samsung.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

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+			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