From: Stephen Boyd <firstname.lastname@example.org> To: Alexandre Belloni <email@example.com>, Sebastian Reichel <firstname.lastname@example.org> Cc: email@example.com, firstname.lastname@example.org, Alessandro Zummo <email@example.com>, Russell King <firstname.lastname@example.org>, Michael Turquette <email@example.com>, firstname.lastname@example.org, email@example.com Subject: Re: [RFCv1] rtc: m41t80: disable clock provider support Date: Fri, 08 Nov 2019 16:24:48 -0800 Message-ID: <20191109002449.534B6207FA@mail.kernel.org> (raw) In-Reply-To: <firstname.lastname@example.org> Quoting Sebastian Reichel (2019-11-08 14:34:15) > Hi, > > On Fri, Nov 08, 2019 at 06:53:29PM +0100, Alexandre Belloni wrote: > > On 08/11/2019 18:01:35+0100, Sebastian Reichel wrote: > > > Congatec's QMX6 system on module (SoM) uses a m41t62 as RTC. The > > > modules SQW clock output defaults to 32768 Hz. This behaviour is > > > used to provide the i.MX6 CKIL clock. Once the RTC driver is probed, > > > the clock is disabled and all i.MX6 functionality depending on > > > the 32 KHz clock have undefined behaviour (e.g. the hardware watchdog > > > run to fast or slow). > > > > > > The normal solution would be to properly describe the clock tree > > > in DT, but from the kernel's perspective this is a chicken-and-egg > > > problem: CKIL is required very early, but the clock is only provided > > > after the I2C RTC has been probed. > > > > > > Technically everything is fine by not touching anything, so this > > > works around the issue by disabling the clock handling from the > > > RTC driver. I guess the proper solution would be to simply mark the > > > clock as always-enabled, but this does not seem to be supported by > > > the clock framework. > > > > > > > You need to have a consumer so this clock is not disabled by the CCF > > after seeing nobody uses it. > > That's why I was wondering if we can have something like regulator's > always-enabled for clocks. There's a flag CLK_IS_CRITICAL that providers can set. > > > If you need it early, you can have a look at rtc-sun6i.c but I > > would like that to not become a recurrent pattern, especially for > > discrete RTCs. > > I don't just need it early. The issue is, that CKIL is the 32khz > low frequency clock fed into the i.MX6. It is initialized by the > clock manager, so I need it before any of the SoC clocks are > registered. Without the SoC clocks, the I2C bus cannot be probed > and thus the RTC driver cannot be probed. > Is this the chicken-egg scenario? I read this thread but I can't follow along with what the problem is. Sorry.
next prev parent reply index Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-11-08 17:01 Sebastian Reichel 2019-11-08 17:53 ` Alexandre Belloni 2019-11-08 22:34 ` Sebastian Reichel 2019-11-09 0:24 ` Stephen Boyd [this message] 2019-11-09 1:41 ` Sebastian Reichel 2019-11-09 6:53 ` Stephen Boyd 2019-11-12 15:15 ` Sebastian Reichel 2019-11-12 22:20 ` Stephen Boyd 2019-11-13 22:27 ` Sebastian Reichel
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