bcm2835: Add Raspberry Pi CPU frequency control to the device tree

This adds a device tree binding for Broadcom BCM2834 CPU frequency control driven via Raspberry Pi VideoCore 4 firmware interface.

---
Depends on the RPi Firmware driver submitted on linux-rpi-kernel a while ago. Can't see it in arm-soc or linux-next yet though (?). Available in branch 'rpi-firmware' of https://github.com/anholt/linux

 .../bindings/cpufreq/raspberrypi,bcm2835-cpufreq.txt        | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/cpufreq/raspberrypi,bcm2835-cpufreq.txt

new file mode 100644
index 0000000..eb126d3
@@ -0,0 +1,13 @@
+Raspberry Pi Broadcom BCM2835 CPU frequency control
+
+Required properties:
+
+- compatible : should be "raspberrypi,bcm2835-cpufreq"
+- firmware : the Raspberry Pi firmware node
+
+Example:
+
+cpufreq {
+        compatible = "raspberrypi,bcm2835-cpufreq";
+        firmware = <&firmware>;
+};

2.4.3

Looks like the firmware driver slipped through the cracks for 4.3. I'll be sending a pull request for it for 4.4.

With the cprman clock driver, we could set CPU frequency natively from Linux. What we get from doing things through the VPU right now are that the MAX (overclock) setting can be set by the user in config.txt, and the VPU does some watching of thermals to decide when to throttle back to non-overclock.

Unless we do native thermal control from Linux (which we don't have a
driver for) to get equivalent protection, then I think we should
probably go ahead with the VPU-based cpufreq control.
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Oh I see; that DT binding was sent as a separate patch rather than part of the series...

DT bindings patches need to be sent to the people/lists in the following MAINTAINERS entry:

OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS

M:      Rob Herring <[email protected]>
M:      Pawel Moll <[email protected]>
M:      Mark Rutland <[email protected]>
M:      Ian Campbell <[email protected]>
M:      Kumar Gala <[email protected]>
L:      devicetree at vger.kernel.org