linux-kernel - [PATCH v6 4/4] clk: dt: Introduce binding for always-on clock support

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Message-Id: <1428432239-4114-5-git-send-email-lee.jones@linaro.org>
Date:	Tue,  7 Apr 2015 19:43:59 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:	lee.jones@...aro.org, kernel@...inux.com, mturquette@...aro.org,
	sboyd@...eaurora.org, devicetree@...r.kernel.org,
	geert@...ux-m68k.org
Subject: [PATCH v6 4/4] clk: dt: Introduce binding for always-on clock support

Signed-off-by: Lee Jones <lee.jones@...aro.org>
---
 .../devicetree/bindings/clock/clock-bindings.txt   | 38 ++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
index 06fc6d5..daf3323 100644
--- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
+++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
@@ -44,6 +44,44 @@ For example:
   clocks by index. The names should reflect the clock output signal
   names for the device.
 
+clock-always-on:    Some hardware contains bunches of clocks which must never be
+		    turned off.  If drivers a) fail to obtain a reference to any
+		    of these or b) give up a previously obtained reference
+		    during suspend, the common clk framework will attempt to
+		    disable them and a platform can fail irrecoverably as a
+		    result.  Usually the only way to recover from these failures
+		    is to reboot.
+
+		    To avoid either of these two scenarios from catastrophically
+		    disabling an otherwise perfectly healthy running system,
+		    clocks can be identified as always-on using this property
+		    from inside a clocksource's node.
+
+		    This property is not to be abused.  It is only to be used to
+		    protect platforms from being crippled by gated clocks, not
+		    as a convenience function to avoid using the framework
+		    correctly inside device drivers.
+
+		    Expected values are hardware clock indices.  If the
+		    clock-indices property (see below) is used, then supplied
+		    values must correspond to one of the listed identifiers.
+		    Using the clock-indices example below, hardware clock <2>
+		    is missing, therefore it is considered invalid to then
+		    list clock <2> as an always-on clock.
+
+For example:
+
+    oscillator {
+        #clock-cells = <1>;
+        clock-output-names = "ckil", "ckih";
+        clock-always-on = <0>, <1>;
+    };
+
+- this node defines a device with two clock outputs, just as in the
+  example above.  The only difference being that 'ckil' and 'ckih'
+  are now identified as an always-on clocks, so the framework will
+  know to never attempt to gate them.
+
 clock-indices:	   If the identifying number for the clocks in the node
 		   is not linear from zero, then this allows the mapping of
 		   identifiers into the clock-output-names array.
-- 
1.9.1

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