On 2018-08-07 09:41, Rob Herring wrote:
On Wed, Aug 01, 2018 at 05:57:41PM -0700, Saravana Kannan wrote:
Many CPU architectures have caches that can scale independent of the
CPUs.
Frequency scaling of the caches is necessary to make sure the cache is
not
a performance bottleneck that leads to poor performance and power. The
same
idea applies for RAM/DDR.
To achieve this, this patch adds a generic devfreq governor that takes
the
current frequency of each CPU frequency domain and then adjusts the
frequency of the cache (or any devfreq device) based on the frequency
of
the CPUs. It listens to CPU frequency transition notifiers to keep
itself
up to date on the current CPU frequency.
To decide the frequency of the device, the governor does one of the
following:
* Uses a CPU frequency to device frequency mapping table
- Either one mapping table used for all CPU freq policies (typically
used
for system with homogeneous cores/clusters that have the same
OPPs).
- One mapping table per CPU freq policy (typically used for ASMP
systems
with heterogeneous CPUs with different OPPs)
OR
* Scales the device frequency in proportion to the CPU frequency. So,
if
the CPUs are running at their max frequency, the device runs at its
max
frequency. If the CPUs are running at their min frequency, the
device
runs at its min frequency. And interpolated for frequencies in
between.
Signed-off-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
---
.../bindings/devfreq/devfreq-cpufreq-map.txt | 53 ++
Bindings should be a separate patch.
drivers/devfreq/Kconfig | 8 +
drivers/devfreq/Makefile | 1 +
drivers/devfreq/governor_cpufreq_map.c | 583
+++++++++++++++++++++
4 files changed, 645 insertions(+)
create mode 100644
Documentation/devicetree/bindings/devfreq/devfreq-cpufreq-map.txt
create mode 100644 drivers/devfreq/governor_cpufreq_map.c
diff --git
a/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq-map.txt
b/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq-map.txt
new file mode 100644
index 0000000..982a30b
--- /dev/null
+++
b/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq-map.txt
@@ -0,0 +1,53 @@
+Devfreq CPUfreq governor
+
+devfreq-cpufreq-map is a parent device that contains one or more
child devices.
+Each child device provides CPU frequency to device frequency mapping
for a
+specific device. Examples of devices that could use this are: DDR,
cache and
+CCI.
+
+Parent device name shall be "devfreq-cpufreq-map".
+
+Required child device properties:
+- cpu-to-dev-map, or cpu-to-dev-map-<X>:
+ A list of tuples where each tuple consists of a
+ CPU frequency (KHz) and the corresponding device
+ frequency. CPU frequencies not listed in the table
+ will use the device frequency that corresponds to the
+ next rounded up CPU frequency.
+ Use "cpu-to-dev-map" if all CPUs in the system should
+ share same mapping.
+ Use cpu-to-dev-map-<cpuid> to describe different
+ mappings for different CPUs. The property should be
+ listed only for the first CPU if multiple CPUs are
+ synchronous.
+- target-dev: Phandle to device that this mapping applies to.
+
+Example:
+ devfreq-cpufreq-map {
+ cpubw-cpufreq {
+ target-dev = <&cpubw>;
+ cpu-to-dev-map =
+ < 300000 1144000 >,
+ < 422400 2288000 >,
+ < 652800 3051000 >,
+ < 883200 5996000 >,
+ < 1190400 8056000 >,
+ < 1497600 10101000 >,
+ < 1728000 12145000 >,
+ < 2649600 16250000 >;
Now we have frequencies listed in multiple places, the OPP tables and
here? Perhaps it is grouping OPPs that should be done.
This doesn't list all OPPs (it can if necessary). This is listing the
minimum frequency needed to give good performance/power for a
device/product.
AFAIK, OPP grouping isn't something that's supported in OPP framework or
in DT. Is there something specific you had in mind? Also, I'd like for
this to work even with devices that don't have OPPs listed in DT.
Thanks,
Saravana
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