Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757216AbbGGPLM (ORCPT ); Tue, 7 Jul 2015 11:11:12 -0400 Received: from mail-yk0-f172.google.com ([209.85.160.172]:33391 "EHLO mail-yk0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932668AbbGGPK6 (ORCPT ); Tue, 7 Jul 2015 11:10:58 -0400 MIME-Version: 1.0 In-Reply-To: <20150707143621.GW18700@pengutronix.de> References: <1434605351-64592-1-git-send-email-eddie.huang@mediatek.com> <20150707130732.GD18561@pengutronix.de> <20150707143621.GW18700@pengutronix.de> From: Daniel Kurtz Date: Tue, 7 Jul 2015 23:10:37 +0800 X-Google-Sender-Auth: LlYbtUEC302ECAzzM4f8LmwWh6c Message-ID: Subject: Re: [PATCH] arm64: dts: mt8173: add clock_null To: Sascha Hauer Cc: Eddie Huang , Matthias Brugger , "open list:OPEN FIRMWARE AND..." , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , linux-mediatek@lists.infradead.org, James Liao 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: 4023 Lines: 90 On Tue, Jul 7, 2015 at 10:36 PM, Sascha Hauer wrote: > On Tue, Jul 07, 2015 at 10:15:29PM +0800, Daniel Kurtz wrote: >> On Tue, Jul 7, 2015 at 9:07 PM, Sascha Hauer wrote: >> > On Thu, Jun 18, 2015 at 01:29:11PM +0800, Eddie Huang wrote: >> >> Add clk_null, which represents clocks that can not / need not >> >> controlled by software. >> >> There are many clocks' parent set to clk_null. >> >> >> >> Signed-off-by: James Liao >> >> Signed-off-by: Eddie Huang >> >> --- >> >> Base on 4.1-rc1 >> >> >> >> Change-Id: I4db9b40d07e28f54f7bae9b676316cbd6a962124 >> >> --- >> >> arch/arm64/boot/dts/mediatek/mt8173.dtsi | 6 ++++++ >> >> 1 file changed, 6 insertions(+) >> >> >> >> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi >> >> index 924fdb6..4798f44 100644 >> >> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi >> >> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi >> >> @@ -81,6 +81,12 @@ >> >> cpu_on = <0x84000003>; >> >> }; >> >> >> >> + clk_null: clk_null { >> >> + compatible = "fixed-clock"; >> >> + clock-frequency = <0>; >> >> + #clock-cells = <0>; >> >> + }; >> > >> > The discussion around this patch shows that we don't want to have this >> > clock in the device tree as it is not a hardware description. >> > >> > Ok, fine. Eddie, you told us that the rate of the current clk_null children >> > is not interesting. What's the motivation to send this patch anyway >> > then? Why can't you keep its children on the orphan list where they are >> > already now? >> > >> > Another possibility would be to instantiate the clk_null clock from C >> > code rather than from the device tree. This way we wouldn't put any >> > wrong descriptions into the device tree and still can implement the >> > support for the real parent clocks when we actually need them. >> >> Some device nodes, like mmc, use a clk_null phandle as one of their clocks: >> >> mmc1: mmc@11240000 { >> compatible = "mediatek,mt8173-mmc", >> "mediatek,mt8135-mmc"; >> reg = <0 0x11240000 0 0x1000>; >> interrupts = ; >> clocks = <&pericfg CLK_PERI_MSDC30_1>, >> <&clk_null>; >> clock-names = "source", "hclk"; >> status = "disabled"; >> }; > > This is another case than the one we discussed about. In the case above > I motivated using a dummy clock since the clock exists in the system, > but is not software controllable. To abstract this from the driver > (which needs this clock since it exists) we here have the dummy clock. > However, of course I can't prove the clock is indeed not software > controllable; that's only the information I have. I was trying to answer your question "What's the motivation to send this patch anyway?". The motivation is to send follow on patches that use the clk_null phandle. We need to provide some clock as the mmc1's hclk. I do not understand why this has to be "clk_null", though. It seems like this should be a real clock coming from one of the real clock_controller nodes. After all, the mmc driver is going to be enabling/disabling this clock for power savings at runtime. What does that even mean for clk_null ? Sorry, I'm not exactly sure what you are saying in your last reply. > > Sascha > > -- > Pengutronix e.K. | | > Industrial Linux Solutions | http://www.pengutronix.de/ | > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- 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/