On Fri, May 30, 2014 at 07:05:43PM +0100, Thomas Abraham wrote:

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.

The mechanism of entry into and exit out of boost mode is outside the
scope of this documentation.

quoted

What are the limitations on boost frequencies? When is a CPU expected to
go to these frequencies and for now long? When should I as a dt author
place elements in boost-frequencies?

I will add these details in the next revision of this patch.

Cheers.

quoted

Why are these in both operating-points and boost-frequencies? It'll be
really easy to accidentally forget to mark something as a
boost-frequency this way. Why not have a boost-points instead?

Does boost-points mean a set of clock speeds which are not listed as
part of operating-points property? If yes, that also is a possible
implementation (it was implemented in one of the earlier version of
this series). Could you confirm that you want the boost mode speeds to
be exclusive of the speeds listed in operating-points?

If these boost mode operating points are not generally advisable for use
as the other operating-points are, then they should IMO been in an
entirely separate property exclusive of (but in the same format as) the
operating-points property, e.g.

operating points = <A B>, <C D>;
boost-points = <E F>;

Otherwise, without boost-mode support we have to parse the boost mode
table to figure out which points to avoid. Or if someone typos a value
in either table we might go into a boost mode when we didn't want to!

Cheers,
Mark.