linux-kernel - [PATCH v4 02/20] PM / devfreq: exynos: Add documentation for generic exynos bus frequency driver

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Message-id: <1450075104-13705-3-git-send-email-cw00.choi@samsung.com>
Date:	Mon, 14 Dec 2015 15:38:06 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	myungjoo.ham@...sung.com, k.kozlowski@...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,
	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: [PATCH v4 02/20] 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>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
---
 .../devicetree/bindings/devfreq/exynos-bus.txt     | 93 ++++++++++++++++++++++
 1 file changed, 93 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..e32daef328da
--- /dev/null
+++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
@@ -0,0 +1,93 @@
+* 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,
+the driver uses the PPMU (Platform Performance Monitoring Unit) which
+is able to measure the current load of sub-blocks.
+
+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.
+- 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 current utilization
+  of buses.
+
+Optional properties for bus device:
+- exynos,saturation-ratio: the percentage value which is used to calibrate
+                   the performance count against 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 (Dynamic Memory Controller) block
+
+	- MIF bus's frequency/voltage table
+	-----------------------
+	|Lv| Freq   | Voltage |
+	-----------------------
+	|L1| 50000  |800000   |
+	|L2| 100000 |800000   |
+	|L3| 134000 |800000   |
+	|L4| 200000 |825000   |
+	|L5| 400000 |875000   |
+	-----------------------
+
+Example2 :
+	The bus of DMC (Dynamic Memory Controller) block in exynos3250.dtsi
+	is 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_table1 {
+		compatible = "operating-points-v2";
+		opp-shared;
+
+		opp@...00000 {
+			opp-hz = /bits/ 64 <50000000>;
+			opp-microvolt = <800000>;
+		};
+		opp@...000000 {
+			opp-hz = /bits/ 64 <100000000>;
+			opp-microvolt = <800000>;
+		};
+		opp@...000000 {
+			opp-hz = /bits/ 64 <134000000>;
+			opp-microvolt = <800000>;
+		};
+		opp@...000000 {
+			opp-hz = /bits/ 64 <200000000>;
+			opp-microvolt = <825000>;
+		};
+		opp@...000000 {
+			opp-hz = /bits/ 64 <400000000>;
+			opp-microvolt = <875000>;
+		};
+	};
+
+	Usage case to handle the frequency and voltage of bus on runtime
+	in exynos3250-rinato.dts is 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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