Re: [PATCHv2 8/8] devfreq: exynos4: Add busfreq driver for exynos4210/exynos4x12

[Kyungmin Park]

On Sat, Mar 15, 2014 at 2:35 AM, Tomasz Figa <t.figa@xxxxxxxxxxx> wrote:
> Hi Chanwoo, Mark,
>
>
> On 14.03.2014 11:56, Chanwoo Choi wrote:
>>
>> Hi Mark,
>>
>> On 03/14/2014 07:35 PM, Mark Rutland wrote:
>>>
>>> On Fri, Mar 14, 2014 at 07:14:37AM +0000, Chanwoo Choi wrote:
>>>>
>>>> Hi Mark,
>>>>
>>>> On 03/14/2014 02:53 AM, Mark Rutland wrote:
>>>>>
>>>>> On Thu, Mar 13, 2014 at 08:17:29AM +0000, Chanwoo Choi wrote:
>>>>>>
>>>>>> This patch add busfreq driver for Exynos4210/Exynos4x12 memory
>>>>>> interface
>>>>>> and bus to support DVFS(Dynamic Voltage Frequency Scaling) according
>>>>>> to PPMU
>>>>>> counters. PPMU (Performance Profiling Monitorings Units) of Exynos4
>>>>>> SoC provides
>>>>>> PPMU counters for DMC(Dynamic Memory Controller) to check memory bus
>>>>>> utilization
>>>>>> and then busfreq driver adjusts dynamically the operating
>>>>>> frequency/voltage
>>>>>> by using DEVFREQ Subsystem.
>>>>>>
>>>>>> Signed-off-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
>>>>>> ---
>>>>>>   .../devicetree/bindings/devfreq/exynos4_bus.txt    | 49
>>>>>> ++++++++++++++++++++++
>>>>>>   1 file changed, 49 insertions(+)
>>>>>>   create mode 100644
>>>>>> Documentation/devicetree/bindings/devfreq/exynos4_bus.txt
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/devfreq/exynos4_bus.txt
>>>>>> b/Documentation/devicetree/bindings/devfreq/exynos4_bus.txt
>>>>>> new file mode 100644
>>>>>> index 0000000..2a83fcc
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/devfreq/exynos4_bus.txt
>>>>>> @@ -0,0 +1,49 @@
>>>>>> +
>>>>>> +Exynos4210/4x12 busfreq driver
>>>>>> +-----------------------------
>>>>>> +
>>>>>> +Exynos4210/4x12 Soc busfreq driver with devfreq for Memory bus
>>>>>> frequency/voltage
>>>>>> +scaling according to PPMU counters of memory controllers
>>>>>> +
>>>>>> +Required properties:
>>>>>> +- compatible   : should contain Exynos4 SoC type as follwoing:
>>>>>> +                 - "samsung,exynos4x12-busfreq" for Exynos4x12
>>>>>> +                 - "samsung,exynos4210-busfreq" for Exynos4210
>>>>>
>>>>>
>>>>> Is there a device called "busfreq"? What device does this binding
>>>>> describe?
>>>>
>>>>
>>>> I'll add detailed description of busfreq as following:
>>>>
>>>> "busfreq(bus frequendcy)" driver means that busfreq driver control
>>>> dynamically
>>>> memory bus frequency/voltage by checking memory bus utilization to
>>>> optimize
>>>> power-consumption. When checking memeory bus utilization,
>>>> exynos4_busfreq driver
>>>> would use PPMU(Performance Profiling Monitoring Units).
>>>
>>>
>>> This still sounds like a description of the _driver_, not the _device_.
>>> The binding should describe the hardware, now the high level abstraction
>>> that software is going to build atop of it.
>>>
>>> It sounds like this is a binding for the DMC PPMU?
>>>
>>> Is the PPMU a component of the DMC, or is it bolted on the side?
>>
>>
>> PPMU(Performance Profiling Monitoring Unit) is to profile performance
>> event of
>> various IP on Exynos4. Each PPMU provide perforamnce event for each IP.
>> We can check various PPMU as following:
>>
>> PPMU_3D
>> PPMU_ACP
>> PPMU_CAMIF
>> PPMU_CPU
>> PPMU_DMC0
>> PPMU_DMC1
>> PPMU_FSYS
>> PPMU_IMAGE
>> PPMU_LCD0
>> PPMU_LCD1
>> PPMU_MFC_L
>> PPMU_MFC_R
>> PPMU_TV
>> PPMU_LEFT_BUS
>> PPMU_RIGHT_BUS
>>
>> DMC (Dynamic Memory Controller) control the operation of DRAM in Exynos4
>> SoC.
>> If we need to get memory bust utilization of DMC, we can get memory bus
>> utilization
>> from PPMU_DMC0/PPMU_DMC1.
>>
>> So, Exynos4's busfreq used two(PPMU_DMC0/PPMU_DMC1) among upper various
>> PPMU list.
>
>
> Well, PPMUs and DMCs are separate hardware blocks found inside Exynos SoCs.
> Busfreq/devfreq is just a Linux-specific abstraction responsible for
> collecting data using PPMUs and controlling frequencies and voltages of
> appropriate power planes, vdd_int responsible for powering DMC0 and DMC1
> blocks in this case.
>
> I'm afraid that the binding you're proposing is unfortunately incorrect,
> because it represents the software abstraction, not the real hardware.
>
> Instead, this should be separated into several independent bindings:
>
>  - PPMU bindings to list all the PPMU instances present in the SoC and
> resources they need,
>
>  - power plane bindings, which define a power plane in which multiple IP
> blocks might reside, can be monitored by one or more PPMU units and
> frequency and voltage of which can be configured according to determined
> performance level. Needed resources will be clocks and regulators to scale
> and probably also operating points.
>
> Then, exynos-busfreq driver should bind to such power planes, parse
> necessary data from DT (list of PPMUs and IP blocks, clocks, regulators and
> operating points) and register a devfreq entity.

How about to use component DT like DRM?
>
> Best regards,
> Tomasz
>
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