Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751709AbbGJILg (ORCPT ); Fri, 10 Jul 2015 04:11:36 -0400 Received: from mail-yk0-f173.google.com ([209.85.160.173]:33924 "EHLO mail-yk0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752462AbbGJILU (ORCPT ); Fri, 10 Jul 2015 04:11:20 -0400 MIME-Version: 1.0 In-Reply-To: <1436513238.10997.12.camel@mtksdaap41> References: <1434605351-64592-1-git-send-email-eddie.huang@mediatek.com> <20150707130732.GD18561@pengutronix.de> <20150707143621.GW18700@pengutronix.de> <1436323041.27396.23.camel@mtksdaap41> <20150708054430.GY18700@pengutronix.de> <1436513238.10997.12.camel@mtksdaap41> From: Daniel Kurtz Date: Fri, 10 Jul 2015 16:11:00 +0800 X-Google-Sender-Auth: KeBqIbHUSV5z_LO2GQViHfvJXSs Message-ID: Subject: Re: [PATCH] arm64: dts: mt8173: add clock_null To: Eddie Huang Cc: Sascha Hauer , "heiko@sntech.de" , Matthias Brugger , "open list:OPEN FIRMWARE AND..." , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mediatek@lists.infradead.org" , =?UTF-8?B?SmFtZXNKSiBMaWFvICjlu5blu7rmmbop?= , "mturquette@gmail.com" , "sboyd@codeaurora.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: 6425 Lines: 142 On Fri, Jul 10, 2015 at 3:27 PM, Eddie Huang wrote: > Hi all, > > On Wed, 2015-07-08 at 13:44 +0800, Sascha Hauer wrote: >> On Wed, Jul 08, 2015 at 10:37:21AM +0800, Eddie Huang wrote: >> > On Tue, 2015-07-07 at 23:10 +0800, Daniel Kurtz wrote: >> > > 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 ? >> > >> > The original purpose of this patch is to provide a common dummy clock >> > for both software don't care clock and clock that is not software >> > controllable.I got comments that device tree should describe hardware >> > and should put exact clock in device tree. I think this is true. So we >> > will remove this clock_null patch, and: >> > >> > 1. For Mediatek SoC CCF driver, James will clarify clock usage further. >> > Actually, we still think it's not necessary to describe whole tree that >> > software don't care, James will deal this in clock driver. >> >> I think that aswell since the device tree is not affected in this case. >> Should we realize later that we indeed need the missing clocks we can >> still implement them without modifying the device tree. >> >> > >> > 2. For other module that use SW not controllable clock (mmc case >> > mentioned by Dan), because this is a real clock, we will put a dummy >> > clock in device tree, like >> > >> > clk_mmchclk: dummyhclk { >> > compatible = "fixed-clock"; >> > clock-frequency = <0>; >> > #clock-cells = <0>; >> > }; >> > >> > How about this modification ? >> >> I wouldn't name it 'dummy', this will again raise some eyebrows. >> > > I got mmc hclk from our designer. HCLK is from AXI Bus directly (sorry, > I gave wrong information to Dan and Sascha yesterday). Because there is > no any mux or gate register to control this HCLK, so current > clk-mt8173.c didn't model it. Since I know where this clock comes from, > I will abandon this stupid dummy clock device tree patch. But there are > two alternative ways: > > 1. In MMC device tree, use parent clock, like > <&topckgen CLK_TOP_AXI_SEL> > > 2. In clk-mt8173.c, add fix factor clock, like apll case > FACTOR(CLK_TOP_APLL1, "apll1_ck", "apll1", 1, 1), > > Either way works, but have different meaning. Any suggestion to handle > thing like this. I like (1), it seems more straightforward. What is the advantage of (2)? Thanks, -Dan > Thanks > Eddie > > -- 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/