linux-kernel - [RFC PATCH 1/3] dt-bindings: Document the STM32F4 clock bindings

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Message-Id: <1432327273-6810-2-git-send-email-daniel.thompson@linaro.org>
Date:	Fri, 22 May 2015 21:41:11 +0100
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Kamil Lulko <rev13@...pl>, Andreas Farber <afaerber@...e.de>,
	linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org
Subject: [RFC PATCH 1/3] dt-bindings: Document the STM32F4 clock bindings

This adds documentation of device tree bindings for the clock related
portions of the STM32 RCC block.

Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
---
 .../devicetree/bindings/clock/st,stm32-rcc.txt     | 65 ++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/st,stm32-rcc.txt

diff --git a/Documentation/devicetree/bindings/clock/st,stm32-rcc.txt b/Documentation/devicetree/bindings/clock/st,stm32-rcc.txt
new file mode 100644
index 0000000..9715d09
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/st,stm32-rcc.txt
@@ -0,0 +1,65 @@
+STMicroelectronics STM32 Reset and Clock Controller
+===================================================
+
+The RCC IP is both a reset and a clock controller. This documentation only
+describes the clock part.
+
+Please also refer to clock-bindings.txt in this directory for common clock
+controller binding usage.
+
+Required properties:
+- compatible: Should be "st,stm32f42xx-rcc"
+- reg: should be register base and length as documented in the
+  datasheet
+- #clock-cells: 2, device nodes should specify the clock in their "clocks"
+  property, containing a phandle to the clock device node, an index selecting
+  between gated clocks and other clocks and an index specifying the clock to
+  use.
+
+Example:
+
+	rcc: rcc@...23800 {
+		#clock-cells = <2>
+		compatible = "st,stm32f42xx-rcc", "st,stm32-rcc";
+		reg = <0x40023800 0x400>;
+	};
+
+Specifying gated clocks
+=======================
+
+The primary index must be set to 0.
+
+The secondary index is the bit number within the RCC register bank, starting
+from the first RCC clock enable register (RCC_AHB1ENR, address offset 0x30).
+
+It is calculated as: index = register_offset / 4 * 32 + bit_offset.
+Where bit_offset is the bit offset within the register (LSB is 0, MSB is 31).
+
+Example:
+
+	/* Gated clock, AHB1 bit 0 (GPIOA) */
+	... {
+		clocks = <&rcc 0 0>
+	};
+
+	/* Gated clock, AHB2 bit 4 (GPIOA) */
+	... {
+		clocks = <&rcc 0 36>
+	};
+
+Specifying other clocks
+=======================
+
+The primary index must be set to 1.
+
+The secondary index is bound with the following magic numbers:
+
+	0	SYSTICK
+	1	FCLK
+
+Example:
+
+	/* Misc clock, FCLK */
+	... {
+		clocks = <&rcc 1 1>
+	};
-- 
2.1.0

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