Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752913AbbBSKgB (ORCPT ); Thu, 19 Feb 2015 05:36:01 -0500 Received: from mail-ob0-f181.google.com ([209.85.214.181]:46833 "EHLO mail-ob0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752351AbbBSKf7 (ORCPT ); Thu, 19 Feb 2015 05:35:59 -0500 MIME-Version: 1.0 In-Reply-To: <20150219102810.GE12212@x1> References: <1424276101-30137-5-git-send-email-lee.jones@linaro.org> <20150218171230.GA30676@x1> <20150218215435.GA32415@x1> <20150219094200.GB12212@x1> <20150219101106.GD12212@x1> <20150219102810.GE12212@x1> Date: Thu, 19 Feb 2015 11:35:58 +0100 X-Google-Sender-Auth: V2w3bgRfsapWEPzA-56IwgFGl9g 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: 3396 Lines: 79 Hi Lee, On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones wrote: > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> 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. > > Okay so ... > > /* > * ICNs are not visible/controllable in Linux, but references to their > * clocks must be obtained and retained or the platform will become > * irrecoverably unresponsive. > */ > interconnects@0 { > compatible = "always-on-clk-domain"; st,...flexgen... > clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>, > <&clk_s_c0_flexgen CLK_ICN_LMI>, > <&clk_s_c0_flexgen CLK_ICN_CPU>, > <&clk_s_c0_flexgen CLK_TX_ICN_DMU>; > }; And then you can have platform code that binds against st,...flexgen..., and enables all referenced clocks. Alternatively, if you have power domains, you can add a reference to the power domain, and let the power domain driver handle it. 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/