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

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Message-ID: <20140314103552.GK25870@e106331-lin.cambridge.arm.com>
Date:	Fri, 14 Mar 2014 10:35:52 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Chanwoo Choi <cw00.choi@...sung.com>
Cc:	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"nm@...com" <nm@...com>,
	"b.zolnierkie@...saung.com" <b.zolnierkie@...saung.com>,
	Pawel Moll <Pawel.Moll@....com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCHv2 8/8] devfreq: exynos4: Add busfreq driver for
 exynos4210/exynos4x12

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@...sung.com>
> >> ---
> >>  .../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?

> 
> 
> > 
> >> +- reg		: offset and length of the ppmudmc0/1
> >> +		  - PPMU (Performance Profiling Monitoring Units)
> > 
> > You seem to require a particular order here. It would be good to be
> > explicit about it.
> 
> OK, I'll modify it as following:
> the offset and length of the PPMU_DMC0 / PPMU_DMC1
> PPMU_DMC0/PPMU_DMC1 show memory buy utilization to exynos4_bus driver.
> 
> > 
> >> +		  : It is to profile performance event of DMC(Dynamic Memory
> >> +		  Controller) So, exynos4_bus.c can check memory bus utilization
> >> +		  by using PPMU of Exynos4 SoC.
> > 
> > This is superfluous, and Linux-specific. The binding document shouldn't
> > need to refer to drivers.
> 
> I'll remove this description.
> 
> > 
> >> +- clocks	: clock number of ppmudmc0/1
> >> +- clock-names	: clock name of ppmudmc0/1
> > 
> > Are these two clocks, or one clock with a slash in the name?
> > 
> > Please list each name separately.
> 
> I'll expalin clocks as following:
> 	"ppmudmc0", "ppmudmc1"
> 
> > 
> >> +- vdd_int-supply: regulator for interface block of Exynos4

How does the interface block relate to the DMC / PPMU?

Cheers,
Mark.
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