linux-kernel - [RFC PATCH 02/15] PM / devfreq: exynos: Add documentation for generic exynos bus frequency driver

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Message-id: <1448545659-32287-3-git-send-email-cw00.choi@samsung.com>
Date:	Thu, 26 Nov 2015 22:47:26 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
	kgene@...nel.org, k.kozlowski@...sung.com
Cc:	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,
	cw00.choi@...sung.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: [RFC PATCH 02/15] PM / devfreq: exynos: Add documentation for generic
 exynos bus frequency driver

This patch adds the documentation for generic exynos bus frequency
driver.

Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
---
 .../devicetree/bindings/devfreq/exynos-bus.txt     | 92 ++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/devfreq/exynos-bus.txt

diff --git a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
new file mode 100644
index 000000000000..5d90623bd173
--- /dev/null
+++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
@@ -0,0 +1,92 @@
+* Generic Exynos Bus frequency device
+
+The Samsung Exynos SoC have many buses for data transfer between DRAM
+and sub-blocks in SoC. Almost Exynos SoC have the common architecture
+for buses. Generally, the each bus of Exynos SoC includes the source clock
+and power line and then is able to change the clock according to the usage
+of each buses on runtime. When gathering the usage of each buses on runtime,
+thie driver uses the exynos-ppmu.c driver with DEVFREQ-EVENT framework.
+
+There are a little different composition among Exynos SoC because each Exynos
+SoC has the different sub-blocks. So, this difference should be specified
+in devicetree file instead of each device driver. In result, this driver
+is able to support the bus frequency for all Exynos SoCs.
+
+Required properties for bus device:
+- compatible: Should be "samsung,exynos-bus".
+- clock-names : the name of clock used by the bus, "bus".
+- clocks : phandles for clock specified in "clock-names" property.
+- #clock-cells: should be 1.
+- operating-points-v2: the OPP table including frequency/voltage information
+  to support DVFS (Dynamic Voltage/Frequency Scaling) feature.
+- vdd-supply: the regulator to provide the buses with the voltage.
+- devfreq-events: the devfreq-event device to monitor the curret utilization
+  of buses.
+
+Optional properties for bus device:
+- exynos,saturation-ratio: the percentage value which is used to calibrate
+                   the performance count againt total cycle count.
+
+Example1:
+	Show the AXI buses of Exynos3250 SoC. Exynos3250 divides the buses to
+	power line (regulator). The MIF (Memory Interface) AXI bus is used to
+	transfer data between DRAM and CPU and uses the VDD_MIF regualtor.
+
+	- power line(VDD_MIF) --> bus for DMC block (dmc clock)
+
+	- MIF bus's frequency/voltage table
+	-----------------------
+	|Lv| Freq   | Voltage |
+	-----------------------
+	|L1| 50000  |800000   |
+	|L2| 100000 |800000   |
+	|L3| 133000 |800000   |
+	|L4| 200000 |800000   |
+	|L5| 400000 |875000   |
+	-----------------------
+
+Example2 :
+	The bus of DMC block in exynos3250.dtsi are listed below:
+
+	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_table0 {
+		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 <133000000>;
+			opp-microvolt = <800000>;
+		};
+		opp03 {
+			opp-hz = /bits/ 64 <200000000>;
+			opp-microvolt = <800000>;
+		};
+		opp04 {
+			opp-hz = /bits/ 64 <400000000>;
+			opp-microvolt = <875000>;
+		};
+	};
+
+	Usage case to handle the frequency and voltage of bus on runtime
+	in exynos3250-rinato.dts are listed below:
+
+	&bus_dmc {
+		devfreq-events = <&ppmu_dmc0_3>, <&ppmu_dmc1_3>;
+		vdd-supply = <&buck1_reg>;	/* VDD_MIF */
+		status = "okay";
+	};
-- 
1.9.1

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