From patchwork Tue Jan 22 06:12:56 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: 2015541 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork1.kernel.org Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) by patchwork1.kernel.org (Postfix) with ESMTP id 82EA33FD1A for ; Tue, 22 Jan 2013 06:21:55 +0000 (UTC) Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1TxXCb-0002HH-9B; Tue, 22 Jan 2013 06:19:21 +0000 Received: from avas-mr21.fibertel.com.ar ([24.232.0.140]) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1TxXCI-0002D9-Vc for linux-arm-kernel@lists.infradead.org; Tue, 22 Jan 2013 06:19:04 +0000 Received: from 201-212-118-238.prima.net.ar ([201.212.118.238]:54730 "EHLO desktop.lan" smtp-auth: "elopez" rhost-flags-OK-OK-OK-FAIL) by avas-mr21.fibertel.com.ar with ESMTPA id S1355270Ab3AVGTC; Tue, 22 Jan 2013 03:19:02 -0300 From: =?UTF-8?q?Emilio=20L=C3=B3pez?= To: Mike Turquette , Subject: [PATCH 3/3] arm: sunxi: Add useful information about sunxi clocks Date: Tue, 22 Jan 2013 03:12:56 -0300 Message-Id: <1358835176-7197-4-git-send-email-emilio@elopez.com.ar> X-Mailer: git-send-email 1.8.1.1 In-Reply-To: <1358835176-7197-1-git-send-email-emilio@elopez.com.ar> References: <1358835176-7197-1-git-send-email-emilio@elopez.com.ar> MIME-Version: 1.0 X-Fib-Al-Info: Al X-Fib-Al-MRId: e2aa9fc704b7adae35d3cdf5779c32d2 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-20130122_011903_447314_E841132B X-CRM114-Status: UNSURE ( 8.99 ) 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 [24.232.0.140 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?= , Maxime Ripard , Stefan Roese , Ezequiel Garcia X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.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