linux-kernel - [PATCH v3 5/5] ARM: dts: sun9i: Add TODO comments for the main and low power clocks

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Message-Id: <1448357536-26613-6-git-send-email-wens@csie.org>
Date:	Tue, 24 Nov 2015 17:32:16 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.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>
Cc:	Chen-Yu Tsai <wens@...e.org>, linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-sunxi@...glegroups.com
Subject: [PATCH v3 5/5] ARM: dts: sun9i: Add TODO comments for the main and low power clocks

The main (24MHz) clock on the A80 is configurable via the PRCM address
space. The low power/speed (32kHz) clock is from an external chip, the
AC100.

Signed-off-by: Chen-Yu Tsai <wens@...e.org>
---
 arch/arm/boot/dts/sun9i-a80.dtsi | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/arm/boot/dts/sun9i-a80.dtsi b/arch/arm/boot/dts/sun9i-a80.dtsi
index a4ce348c0831..eb69a62f6bc4 100644
--- a/arch/arm/boot/dts/sun9i-a80.dtsi
+++ b/arch/arm/boot/dts/sun9i-a80.dtsi
@@ -128,6 +128,17 @@
 		 */
 		ranges = <0 0 0 0x20000000>;
 
+		/*
+		 * This clock is actually configurable from the PRCM address
+		 * space. The external 24M oscillator can be turned off, and
+		 * the clock switched to an internal 16M RC oscillator. Under
+		 * normal operation there's no reason to do this, and the
+		 * default is to use the external good one, so just model this
+		 * as a fixed clock. Also it is not entirely clear if the
+		 * osc24M mux in the PRCM affects the entire clock tree, which
+		 * would also throw all the PLL clock rates off, or just the
+		 * downstream clocks in the PRCM.
+		 */
 		osc24M: osc24M_clk {
 			#clock-cells = <0>;
 			compatible = "fixed-clock";
@@ -135,6 +146,13 @@
 			clock-output-names = "osc24M";
 		};
 
+		/*
+		 * The 32k clock is from an external source, normally the
+		 * AC100 codec/RTC chip. This clock is by default enabled
+		 * and clocked at 32768 Hz, from the oscillator connected
+		 * to the AC100. It is configurable, but no such driver or
+		 * bindings exist yet.
+		 */
 		osc32k: osc32k_clk {
 			#clock-cells = <0>;
 			compatible = "fixed-clock";
-- 
2.6.2

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