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Subject[PATCH v6 02/21] PM / devfreq: exynos: Add documentation for generic exynos bus frequency driver
Date
This patch adds the documentation for generic exynos bus frequency
driver.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
---
.../devicetree/bindings/devfreq/exynos-bus.txt | 95 ++++++++++++++++++++++
1 file changed, 95 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..78171b918e3f
--- /dev/null
+++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
@@ -0,0 +1,95 @@
+* Generic Exynos Bus frequency device
+
+The Samsung Exynos SoC has many buses for data transfer between DRAM
+and sub-blocks in SoC. Most Exynos SoCs share the common architecture
+for buses. Generally, each bus of Exynos SoC includes a source clock
+and a power line, which are able to change the clock frequency
+of the bus in runtime. To monitor the usage of each bus in 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 different sub-blocks. Therefore, shch 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.
+- exynos,voltage-tolerance: the percentage value for bus voltage tolerance
+ which is used to calculate the max voltage.
+
+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@50000000 {
+ opp-hz = /bits/ 64 <50000000>;
+ opp-microvolt = <800000>;
+ };
+ opp@100000000 {
+ opp-hz = /bits/ 64 <100000000>;
+ opp-microvolt = <800000>;
+ };
+ opp@134000000 {
+ opp-hz = /bits/ 64 <134000000>;
+ opp-microvolt = <800000>;
+ };
+ opp@200000000 {
+ opp-hz = /bits/ 64 <200000000>;
+ opp-microvolt = <825000>;
+ };
+ opp@400000000 {
+ 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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