On 11/26/2014 12:49 AM, Viresh Kumar wrote:
Fixing Santosh's email id as he switched employer ..
Yeah I did ;-)
On 26 November 2014 at 14:16, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
DT based cpufreq drivers doesn't require much support from platform code now a
days as most of the stuff is moved behind generic APIs. Like clk APIs for
changing clock rates, regulator APIs for changing voltages, etc.
One of the bottleneck still left was how to select which cpufreq driver to probe
for a given platform as there might be multiple drivers available.
Traditionally, we used to create platform devices from machine specific code
which binds with a cpufreq driver. And while we moved towards DT based device
creation, these devices stayed as is.
The problem is getting worse now as we have architectures now with Zero platform
specific code. Forcefully these platforms have to create a new file in
drivers/cpufreq/ to just add these platform devices in order to use the generic
drivers like cpufreq-dt.c.
We should definitely avoid that since that code is just pointless. Good
to see that you picked up that.
This has been discussed again and again, but with no solution yet. Last it was
discussed here:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/256154.html
This patch is an attempt towards getting the bindings.
We only need to have one entry in cpus@cpu0 node which will match with drivers
name.
We can then add another file drivers/cpufreq/device_dt.c, which will add a
platform device with the name it finds from cpus@cpu0 node and existing drivers
will work without any change. Or something else if somebody have a better
proposal. But lets fix the bindings first.
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
.../devicetree/bindings/cpufreq/drivers.txt | 53 ++++++++++++++++++++++
1 file changed, 53 insertions(+)
create mode 100644 Documentation/devicetree/bindings/cpufreq/drivers.txt
diff --git a/Documentation/devicetree/bindings/cpufreq/drivers.txt b/Documentation/devicetree/bindings/cpufreq/drivers.txt
new file mode 100644
index 0000000..bd14917
--- /dev/null
+++ b/Documentation/devicetree/bindings/cpufreq/drivers.txt
@@ -0,0 +1,53 @@
+Binding to select which cpufreq driver to register
+
+It is a generic DT binding for selecting which cpufreq-driver to register for
+any platform.
+
+The property listed below must be defined under node /cpus/cpu@0 node. We don't
+support multiple CPUFreq driver currently for different cluster and so this
+information isn't required to be present in CPUs of all clusters.
+
+Required properties:
+- None
+
+Optional properties:
+- dvfs-method: CPUFreq driver to probe. For example: "arm-bL-cpufreq-dt",
+ "cpufreq-dt", etc
+
+Examples:
+
+cpus {
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ cpu@0 {
+ compatible = "arm,cortex-a9";
+ reg = <0>;
+ next-level-cache = <&L2>;
+ operating-points = <
+ /* kHz uV */
+ 792000 1100000
+ 396000 950000
+ 198000 850000
+ >;
+ dvfs-method = "cpufreq-dt";
+ };
Its really not 'dvfs-method' but really the actual driver which you
want to probe. Also we should just have one global way to parse
DT vs non-DT cpufreq drivers. In other words, instead of matching
multiple driver strings for different drivers, we should come up with
slightly generic binding. Probably 'cpufreq-dt' for all DT based probed
CPUFREQ drivers.
What you say ?
Regards,
Santosh
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