Re: [PATCH v2 09/19] PM / devfreq: exynos: Update documentation for bus devices using passive governor

From: Chanwoo Choi <cwchoi00@gmail.com>
To: Rob Herring <robh@kernel.org>
Cc: "myungjoo.ham@samsung.com" <myungjoo.ham@samsung.com>,
	"Krzysztof Kozłowski" <k.kozlowski@samsung.com>,
	"Kukjin Kim" <kgene@kernel.org>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"Pawel Moll" <pawel.moll@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Ian Campbell" <ijc+devicetree@hellion.org.uk>,
	"Kumar Gala" <galak@codeaurora.org>,
	"Russell King - ARM Linux" <linux@arm.linux.org.uk>,
	tjakobi@math.uni-bielefeld.de, linux.amoon@gmail.com,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	devicetree <devicetree@vger.kernel.org>
Subject: Re: [PATCH v2 09/19] PM / devfreq: exynos: Update documentation for bus devices using passive governor
Date: Fri, 11 Dec 2015 00:10:13 +0900	[thread overview]
Message-ID: <CAGTfZH0T8ufrBKT3vKoivk5Vn_AUHnB+or0QRgr=D77q7puAJA@mail.gmail.com> (raw)
In-Reply-To: <20151210142109.GA32109@rob-hp-laptop>

On Thu, Dec 10, 2015 at 11:21 PM, Rob Herring <robh@kernel.org> wrote:
> On Wed, Dec 09, 2015 at 01:08:01PM +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@samsung.com>
>> ---
>>  .../devicetree/bindings/devfreq/exynos-bus.txt     | 244 ++++++++++++++++++++-
>>  1 file changed, 241 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>> index 54a1f9c46c88..c4fdc70f8eac 100644
>> --- a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>> +++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>> @@ -13,18 +13,23 @@ 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.
>>
>> @@ -33,7 +38,20 @@ 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 (Dynamic Memory Controller) block
>> +     - MIF (Memory Interface) block
>> +     : VDD_MIF |--- DMC (Dynamic Memory Controller)
>> +
>> +     - INT (Internal) block
>> +     : VDD_INT |--- LEFTBUS (parent device)
>> +               |--- PERIL
>> +               |--- MFC
>> +               |--- G3D
>> +               |--- RIGHTBUS
>> +               |--- FSYS
>> +               |--- LCD0
>> +               |--- PERIR
>> +               |--- ISP
>> +               |--- CAM
>
> This still has the same problem as before. I would expect that the bus
> hierarchy in the dts match the hierarchy here. You just have flat nodes
> in the example below. So all IP blocks affected by frequency scaling
> should be under the bus node defining the OPPs. Something like this:

The each bus of sub-block has not h/w dependency among sub-blocks
and has the owned source clock / OPP table. Just they share the same
power line. So, I think that flat nodes in the example below is not problem.

Because of using the same power line, the sub-blocks would be tied
by devfreq framework only for the behavior of bus frequency scaling .

>
> soc {
>         compatible = "simple-bus";
>         bus {
>                 compatible = "my-awesome-dvfs-bus"; /* simple-bus too if
> no setup needed first */
>                 reg = <0x0 0x0>; // Bus control registers
>                 clocks = <&ccm BUS_CLK>;
>                 operating-points-v2 = <&opp>;
>                 device@0 {
>                         compatible = "my-awesome-device-1";
>                 };
>                 device@1 {
>                         compatible = "my-awesome-device-2";
>                 };
>         };
> };