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SubjectRe: [RFC PATCH 02/15] PM / devfreq: exynos: Add documentation for generic exynos bus frequency driver
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Hi Rob,

On Sat, Nov 28, 2015 at 5:30 AM, Rob Herring <robh@kernel.org> wrote:
> On Thu, Nov 26, 2015 at 10:47:26PM +0900, Chanwoo Choi wrote:
>> This patch adds the documentation for generic exynos bus frequency
>> driver.
>>
>> Signed-off-by: Chanwoo Choi <cw00.choi@samsung.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.
>
> Please don't refer to Linux subsystem specifics in bindings. It looks
> like you are creating devices to match what you have for drivers, not
> what the h/w looks like.

OK. I'll modify it on next patchiest.

>
>
>> +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:
>
> What is DMC?

DMC (DRAM Memory Controller)

>
>> +
>> + bus_dmc: bus_dmc {
>> + compatible = "samsung,exynos-bus";
>
> I would expect the children of this bus to be under this node.

I add the detailed description on patch9 which is included in this
patch-set as follwoing.
- [RFC PATCH 09/15] PM / devfreq: exynos: Update documentation for bus
devices usingpassive governor

This patch-set don' include the the list of children node in parent dt node.
Instead, I add the separate node and then each children node has the
the phandle of parent node

>
>> + 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>;
>
> What do these phandles point to exactly?

DMC (DRAM Memory Controller) bus need to gather the current load in
bus on runtime.
The Exynos SoC has the PPMU (Platform Performance Monitoring Unit) for
sub-blocks.
The "ppmu_dmc0_3" and "ppmu_dmc1_3" measure the current load in DMC bus
with DEVFREQ-EVENT framework.

So, "bus_dmc" uses the load result from "ppmu_dmc0_3" and
"ppmu_dmc1_3" when deciding
the next bus frequency as basis data of dmc bus.

>
>> + vdd-supply = <&buck1_reg>; /* VDD_MIF */
>> + status = "okay";
>> + };
>> --
>> 1.9.1


Regards,
Chanwoo Choi


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