Some platforms require select clock to be always running, e.g. because
those clock supply vital devices which are not otherwise attached to
the system and thus do not have a matching DT node and clock consumer.
An example is a system where the SoC serves as a crystal oscillator
replacement for a programmable logic device. The "critical-clocks"
property of a clock controller allows listing clock which must never
be turned off.
Clock listed in the "critical-clocks" property may have other consumers
in DT, listing the clock in "critical-clocks" only assures those clock
are never turned off, and none of these optional additional consumers
can turn the clock off either.
The implementation is modeled after "protected-clocks".
Signed-off-by: Marek Vasut <marex@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michael Turquette <mturquette@xxxxxxxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
Cc: devicetree@xxxxxxxxxxxxxxx
To: linux-clk@xxxxxxxxxxxxxxx
---
V2: Update the commit message to clarify the behavior
V3: s@Some platforms require clock@Some platforms require some clocks@
---
.../devicetree/bindings/clock/clock-bindings.txt | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
index f2ea53832ac63..d7f7afe2cbd0c 100644
--- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
+++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
@@ -169,6 +169,22 @@ a shared clock is forbidden.
Configuration of common clocks, which affect multiple consumer devices can
be similarly specified in the clock provider node.
+==Critical clocks==
+
+Some platforms require some clocks to be always running, e.g. because those
+clock supply devices which are not otherwise attached to the system. One
+example is a system where the SoC serves as a crystal oscillator replacement
+for a programmable logic device. The critical-clocks property of a clock
+controller allows listing clock which must never be turned off.
+
+ clock-controller@a000f000 {
+ compatible = "vendor,clk95;
+ reg = <0xa000f000 0x1000>
+ #clocks-cells = <1>;
+ ...
+ critical-clocks = <UART3_CLK>, <SPI5_CLK>;
+ };
+
==Protected clocks==
Some platforms or firmwares may not fully expose all the clocks to the OS, such
--
2.35.1
