[PATCH v2 1/2] dt-bindings: clk: Introduce 'critical-clocks' property

[Marek Vasut <marex@denx.de>]

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@denx.de>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: devicetree@vger.kernel.org
To: linux-clk@vger.kernel.org
---
V2: Update the commit message to clarify the behavior
---
 .../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..975230e603d12 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 clock 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