linux-kernel - Re: [RFC PATCH 09/15] PM / devfreq: exynos: Update documentation for bus devices using passive governor

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Date:	Wed, 02 Dec 2015 10:41:47 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Rob Herring <robh@...nel.org>
Cc:	myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
	kgene@...nel.org, k.kozlowski@...sung.com, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux@....linux.org.uk,
	tjakobi@...h.uni-bielefeld.de, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [RFC PATCH 09/15] PM / devfreq: exynos: Update documentation for
 bus devices using passive governor

Hi Rob,

I'm sorry for delay reply due to the problem of email system
on the company.

On 2015년 12월 01일 06:14, Rob Herring wrote:
> On Thu, Nov 26, 2015 at 10:47:33PM +0900, Chanwoo Choi wrote:
>> This patch updates the documentation for passive bus devices and adds the
>> detailed example of Exynos3250.
>>
>> Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
>> ---
>>  .../devicetree/bindings/devfreq/exynos-bus.txt     | 226 ++++++++++++++++++++-
>>  1 file changed, 223 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>> index 5d90623bd173..c4a6fe30075e 100644
>> --- a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>> +++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>> @@ -12,18 +12,23 @@ 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:
>> +Required properties for all bus devices:
>>  - 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.
>> +
>> +Required properties for only parent bus device:
>>  - 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:
>> +Required properties for only passive bus device:
>> +- devfreq: the parent bus device.
>> +
>> +Optional properties for only parent bus device:
>>  - exynos,saturation-ratio: the percentage value which is used to calibrate
>>                     the performance count againt total cycle count.
>>  
>> @@ -32,7 +37,19 @@ Example1:
>>  	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 (Memory Interface) block
>> +	: VDD_MIF |--- DMC
>> +
>> +	- INT (Internal) block
>> +	: VDD_INT |--- LEFTBUS  |--- PERIL
>> +		  |    (parent) |--- MFC
>> +		  |             |--- G3D
>> +		  |
>> +		  |--- RIGHTBUS |--- FSYS
>> +				|--- LCD0
>> +				|--- PERIR
>> +				|--- ISP
>> +				|--- CAM
> 
> I would expect the DT to mirror this topology which doesn't seem to be 
> the case in the example.

You're right. The above topology is not appropriate to show the correlation
between power line and sub blocks. I'll modify it as following.

The all blocks which are included in the INT (internal) block
share the one power line (VDD_INT).


	VDD_MIF |--- DMC

	VDD_INT |--- LEFTBUS
		|--- PERIL
		|--- MFC
		|--- G3D
		|--- RIGHTBUS
		|--- FSYS
		|--- LCD0
		|--- PERIR
		|--- ISP
		|--- CAM

> 
> 
>>  	- MIF bus's frequency/voltage table
>>  	-----------------------
>> @@ -45,6 +62,20 @@ Example1:
>>  	|L5| 400000 |875000   |
>>  	-----------------------
>>  
>> +	- INT bus's frequency/voltage table
>> +	-----------------------------------------------------------------------
>> +	|Lv| Freq                                                   | Voltage |
>> +	-----------------------------------------------------------------------
>> +	|  |LEFTBUS|RIGHTBUS|LCD0   |FSYS   |MCUISP |ISP    |PERIL  |VDD_INT  |
>> +	|  |*parent|passive |passive|passive|passive|passive|passive|         |
>> +	-----------------------------------------------------------------------
>> +	|L1|50000  |50000   |50000  |50000  |50000  |50000  |50000  |900000   |
>> +	|L2|80000  |80000   |80000  |80000  |80000  |80000  |80000  |900000   |
>> +	|L3|100000 |100000  |100000 |100000 |100000 |100000 |100000 |1000000  |
>> +	|L4|133000 |133000  |133000 |133000 |200000 |200000 |       |1000000  |
>> +	|L5|200000 |200000  |200000 |200000 |400000 |300000 |       |1000000  |
>> +	-----------------------------------------------------------------------
> 
> Do you really have 5 states? It look like there are 2 to me because the 
> OPP tables only really need to have the max freq at each voltage point. 

I'm sure. The OPP allow OPP table to add the same voltage for each OPP entry.
Instead, OPP don't permit adding the duplicate frequency. If OPP table includes
the different frequency as OPP entry, there is no problem. It is tested.

Regards,
Chanwoo Choi


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