Re: [PATCHv2 8/8] devfreq: exynos4: Add busfreq driver for exynos4210/exynos4x12
From: Tomasz Figa
Date: Sat Mar 15 2014 - 08:41:58 EST
On 15.03.2014 12:36, Kyungmin Park wrote:
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?
Well, basically this is what I proposed. Each "power plane" would be a
"subsystem" built from components - PPMUs, IP blocks, clocks,
regulators, etc, specified in DT by existing means, e.g.
ppmu_disp: ppmu@12340000 {
/* Resources of PPMU */
}
fimd: fimd@23450000 {
/* Resources of FIMD */
};
power-plane-display {
compatible = "samsung,power-plane";
samsung,ppmus = <&ppmu_disp>, ...;
samsung,devices = <&fimd>, ...;
clock-names = "aclk_xxx", "sclk_xxx", ...;
clocks = ...;
vdd_xxx-supply = ...;
};
However I'm still wondering whether there shouldn't be a relation
between power planes and power domains and simply existing power domain
nodes shouldn't be extended with the data I put above in
power-plane-display node. I need to check this in the documentation back
at work on Monday.
Best regards,
Tomasz
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