Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752899AbbBSKSd (ORCPT ); Thu, 19 Feb 2015 05:18:33 -0500 Received: from mail-ob0-f179.google.com ([209.85.214.179]:47751 "EHLO mail-ob0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752440AbbBSKSb (ORCPT ); Thu, 19 Feb 2015 05:18:31 -0500 MIME-Version: 1.0 In-Reply-To: <20150219101106.GD12212@x1> References: <1424276101-30137-1-git-send-email-lee.jones@linaro.org> <1424276101-30137-5-git-send-email-lee.jones@linaro.org> <20150218171230.GA30676@x1> <20150218215435.GA32415@x1> <20150219094200.GB12212@x1> <20150219101106.GD12212@x1> Date: Thu, 19 Feb 2015 11:18:30 +0100 X-Google-Sender-Auth: WQ03EQkG_5eZHApT2ILpROHaKPI Message-ID: Subject: Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation From: Geert Uytterhoeven To: Lee Jones Cc: Rob Herring , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Mike Turquette , Stephen Boyd , kernel@stlinux.com, "devicetree@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2427 Lines: 53 Hi Lee, On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones wrote: > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones wrote: >> >> What kind of clocks are these? What do they control? >> >> Memory controllers? Bus controllers? >> >> >> >> They must control some device(s), so there should be one or more device >> >> nodes in DT that reference these clocks. >> >> As soon as that information is in DT, support can be added to Linux to >> >> make sure the "critical" clocks stay enabled, either through a real driver, >> >> or through platform code. >> > >> > Some do, some don't. For instance, we have one clock which controls >> > SPI and I2C that must not be turned off. We discovered this then when >> > a suspend was attempted and the board refused to resume. This clock >> > also runs one of the critical interconnects that runs from the a9. It >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C >> > drivers because the same IP on another board might be controlled by a >> > different clock which is able to be gated. >> > >> > There are also clocks which control other interconnects that are not >> > connected to any device drivers. If we fail to take references for >> > them before clk_disable_unused() is called, again the board hangs. We >> > even lose JTAG support. >> >> Interconnects are buses. Can't you represent those buses in the DT >> hierarchy, and give them clocks properties? > > So instead of this nice succinct, simple, cover all bases > (interconnects was just an example, there are bound to be others), > generic framework, you are suggesting to write drivers for devices > which other than "don't turn my clocks off", Linux can't actually see > or control? DT describes the hardware, not behavior. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/