From patchwork Mon Feb 25 14:44:28 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Emilio_L=C3=B3pez?= X-Patchwork-Id: 222926 Return-Path: X-Original-To: incoming-imx@patchwork.ozlabs.org Delivered-To: patchwork-incoming-imx@bilbo.ozlabs.org Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:4978:20e::2]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 7A2112C02A3 for ; Tue, 26 Feb 2013 01:54:18 +1100 (EST) Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1U9zOf-0006Zu-By; Mon, 25 Feb 2013 14:51:17 +0000 Received: from avas-mr18.fibertel.com.ar ([24.232.0.121]) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1U9zO3-0006KZ-4D for linux-arm-kernel@lists.infradead.org; Mon, 25 Feb 2013 14:50:40 +0000 Received: from 201-212-118-238.prima.net.ar ([201.212.118.238]:32941 "EHLO desktop.lan" smtp-auth: "elopez" rhost-flags-OK-OK-OK-FAIL) by avas-mr18.fibertel.com.ar with ESMTPA id S751690Ab3BYOu3; Mon, 25 Feb 2013 11:50:29 -0300 From: =?UTF-8?q?Emilio=20L=C3=B3pez?= To: Gregory CLEMENT , Mike Turquette , Maxime Ripard Subject: [PATCH v2 3/3] arm: sunxi: Add useful information about sunxi clocks Date: Mon, 25 Feb 2013 11:44:28 -0300 Message-Id: <1361803468-9899-4-git-send-email-emilio@elopez.com.ar> X-Mailer: git-send-email 1.8.2.rc0 In-Reply-To: <1361803468-9899-1-git-send-email-emilio@elopez.com.ar> References: <1358835176-7197-1-git-send-email-emilio@elopez.com.ar> <1361803468-9899-1-git-send-email-emilio@elopez.com.ar> MIME-Version: 1.0 X-Fib-Al-Info: Al X-Fib-Al-MRId: a109f2d6e5708523a96008f0aab64447 X-Fib-Al: noav X-Fib-Al-SA: analyzed X-Fib-Al-From: emilio@elopez.com.ar X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20130225_095039_595915_49FF55CA X-CRM114-Status: UNSURE ( 8.71 ) X-CRM114-Notice: Please train this message. X-Spam-Score: 3.3 (+++) X-Spam-Report: SpamAssassin version 3.3.2 on merlin.infradead.org summary: Content analysis details: (3.3 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [24.232.0.121 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] 2.5 TAB_IN_FROM From starts with a tab 2.8 KB_DATE_CONTAINS_TAB KB_DATE_CONTAINS_TAB Cc: Alejandro Mery , =?UTF-8?q?Emilio=20L=C3=B3pez?= , Ezequiel Garcia , Stefan Roese , linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.14 Precedence: list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+incoming-imx=patchwork.ozlabs.org@lists.infradead.org List-Id: linux-imx-kernel.lists.patchwork.ozlabs.org This patch contains useful bits of information about the sunxi clocks that may help and/or be interesting for current and future developers. Signed-off-by: Emilio López --- Documentation/arm/sunxi/clocks.txt | 56 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 Documentation/arm/sunxi/clocks.txt diff --git a/Documentation/arm/sunxi/clocks.txt b/Documentation/arm/sunxi/clocks.txt new file mode 100644 index 0000000..e09a88a --- /dev/null +++ b/Documentation/arm/sunxi/clocks.txt @@ -0,0 +1,56 @@ +Frequently asked questions about the sunxi clock system +======================================================= + +This document contains useful bits of information that people tend to ask +about the sunxi clock system, as well as accompanying ASCII art when adequate. + +Q: Why is the main 24MHz oscillator gatable? Wouldn't that break the + system? + +A: The 24MHz oscillator allows gating to save power. Indeed, if gated + carelessly the system would stop functioning, but with the right + steps, one can gate it and keep the system running. Consider this + simplified suspend example: + + While the system is operational, you would see something like + + 24MHz 32kHz + | + PLL1 + \ + \_ CPU Mux + | + [CPU] + + When you are about to suspend, you switch the CPU Mux to the 32kHz + oscillator: + + 24Mhz 32kHz + | | + PLL1 | + / + CPU Mux _/ + | + [CPU] + + Finally you can gate the main oscillator + + 32kHz + | + | + / + CPU Mux _/ + | + [CPU] + +Q: Were can I learn more about the sunxi clocks? + +A: The linux-sunxi wiki contains a page documenting the clock registers, + you can find it at + + http://linux-sunxi.org/A10/CCM + + The authoritative source for information at this time is the ccmu driver + released by Allwinner, you can find it at + + https://github.com/linux-sunxi/linux-sunxi/tree/sunxi-3.0/arch/arm/mach-sun4i/clock/ccmu