[PATCH v6 2/2] Documentation: devicetree: Add boost-frequency binding to list boost mode frequency

On 30.05.2014 20:33, Thomas Abraham wrote:

On Fri, May 30, 2014 at 11:45 PM, Tomasz Figa [off-list ref] wrote:

quoted

On 30.05.2014 20:05, Thomas Abraham wrote:

quoted

Hi Mark,

On Fri, May 30, 2014 at 6:38 PM, Mark Rutland [off-list ref] wrote:

quoted

Hi,

Apologies for being somewhat late w.r.t. review on this.

On Fri, May 30, 2014 at 10:01:17AM +0100, Thomas Abraham wrote:

quoted

From: Thomas Abraham <redacted>

Add a new optional boost-frequency binding for specifying the frequencies
usable in boost mode.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <redacted>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <redacted>
Cc: Kumar Gala <redacted>
Signed-off-by: Thomas Abraham <redacted>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Lukasz Majewski <redacted>
---
 .../devicetree/bindings/cpufreq/cpufreq-boost.txt  |   38 ++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt

diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt b/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt
new file mode 100644
index 0000000..63ed0fc
--- /dev/null
+++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt

@@ -0,0 +1,38 @@
+* Device tree binding for CPU boost frequency (aka over-clocking)
+
+Certain CPU's can be operated in optional 'boost' mode (or sometimes referred as

Nit: CPUs (we're not greengrocers [1])

quoted

+overclocking) in which the CPU can operate at frequencies which are not
+specified by the manufacturer as CPU's operating frequency.
+
+Optional Properties:
+- boost-frequencies: list of frequencies in KHz to be used only in boost mode.
+  This list should be a subset of frequencies listed in "operating-points"
+  property. Refer to Documentation/devicetree/bindings/power/opp.txt for
+  details about "operating-points" property.

What is 'boost-mode'?

boost-mode activates additional one or more cpu clock speeds (which
are not specified as operating frequency of the cpu by the
manufacturer). The cpu is allowed to operate in these boost mode
speeds when the boost mode is active. The boost mode speeds are
usually undocumented. Some of the chip samples could be clocked in
boost mode speeds and only such samples can be safely operated in
boost mode.

IMHO the most important part that I believe should be stated in the
documentation is that CPU usually can operate in boost mode for limited
amount of time, which depends on thermal conditions, which makes the
boost operating points separate from normal ones, which can be used at
any time.

The factors that allow a CPU to operate in boost mode and the duration
the CPU can operate in boost mode clock speed is a CPU specific
description. This binding does not describe such CPU specific
behavior. This binding only states the additional clock speeds CPU is
allowed to operate in boost mode. The boost mode entry and exit
conditions are implementation specific and not part of the scope of
this binding and documentation.

The binding documentation describes properties related to boost mode and
so it must explain what boost mode is, otherwise those properties will
not make any sense. I'm not saying that specific constraints must be
listed, but the text should mention that those operating points might
need some.

Best regards,
Tomasz