Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756835Ab3DWPsA (ORCPT ); Tue, 23 Apr 2013 11:48:00 -0400 Received: from h1446028.stratoserver.net ([85.214.92.142]:49295 "EHLO mail.ahsoftware.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756559Ab3DWPr6 (ORCPT ); Tue, 23 Apr 2013 11:47:58 -0400 Message-ID: <5176AD08.8090108@ahsoftware.de> Date: Tue, 23 Apr 2013 17:47:20 +0200 From: Alexander Holler User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130402 Thunderbird/17.0.5 MIME-Version: 1.0 To: Andrew Morton CC: linux-kernel@vger.kernel.org, rtc-linux@googlegroups.com, Alessandro Zummo , Lars-Peter Clausen , Jonathan Cameron , Jiri Kosina Subject: Re: [PATCH 3/3] rtc: rtc-hid-sensor-time; add option hctosys to set time at boot References: <1366384452-14367-1-git-send-email-holler@ahsoftware.de> <1366384452-14367-4-git-send-email-holler@ahsoftware.de> <20130422163830.4aaaef240b1572dc778dd620@linux-foundation.org> <51764B8E.9090402@ahsoftware.de> <51765D8C.1010008@ahsoftware.de> <51765ECD.6020601@ahsoftware.de> <51765FB9.2050009@ahsoftware.de> In-Reply-To: <51765FB9.2050009@ahsoftware.de> Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4117 Lines: 94 Am 23.04.2013 12:17, schrieb Alexander Holler: > Am 23.04.2013 12:13, schrieb Alexander Holler: >> Am 23.04.2013 12:08, schrieb Alexander Holler: >>> Am 23.04.2013 10:51, schrieb Alexander Holler: >>>> Am 23.04.2013 01:38, schrieb Andrew Morton: >>>>> On Fri, 19 Apr 2013 17:14:12 +0200 Alexander Holler >>>>> wrote: >>>>> >>>>>> drivers/rtc/hctosys (CONFIG_RTC_HCTOSYS) doesn't work for >>>>>> rtc-hid-sensor-time because it will be called in late_init, and thus >>>>>> before >>>>>> rtc-hid-sensor-time gets loaded. >>>>> >>>>> Isn't that true of all RTC drivers which are built as modules? >>>>> There's >>>>> nothing special about hid-sensor-time here? >>>>> >>>>> I assume the standard answer here is "your RTC driver should be built >>>>> into vmlinux". If we wish to make things work for modular RTC drivers >>>>> then we should find a solution which addresses *all* RTC drivers? >>>> >>>> No. I having rtc-hid-sensor-time, hid-sensor-hub (and USB) statically >>>> linked in doesn't help. Here is what happens here with such an >>>> configuration: >>>> >>>> -- >>>> [ 7.638970] drivers/rtc/hctosys.c: unable to open rtc device (rtc0) >>>> [ 7.645639] Waiting 180sec before mounting root device... >>>> [ 16.598759] HID-SENSOR-2000a0 HID-SENSOR-2000a0.0: rtc core: >>>> registered hid-sensor-time as rtc0 >>>> [ 16.608712] HID-SENSOR-2000a0 HID-SENSOR-2000a0.0: hctosys: setting >>>> system clock to 2013-04-19 16:45:06 UTC (1366389906) >>>> -- >>>> >>>> I havent't looked in detail at why rtc-hid-sensor-time gets loaded that >>>> late, but I assume it's because the USB stack (and/or the device or the >>>> communication inbetween) needs some time (and I assume that's why >>>> rootwait and rootdelay got invented too). >>>> >>>>> >>>>>> To set the time through rtc-hid-sensor-time >>>>>> at startup, the module now checks by default if the system time is >>>>>> before >>>>>> 1970-01-02 and sets the system time (once) if this is the case. >>>>>> >>>>>> To disable this behaviour, set the module option hctosys to zero, >>>>>> e.g. by >>>>>> using rtc-hid-sensor-time.hctosys=0 at the kernel command line if the >>>>>> driver is statically linked into the kernel. >>>>> >>>>> Is a bit hacky, no? >>>> >>>> I didn't have any other idea to prevent an USB (or any other >>>> hot-pluggable HID) device to change the time while still beeing able >>>> (by >>>> default) to set the time by such an device at boot. But I'm open to >>>> suggestions. (E.g. one of the scenarios I want to prevent is, that a >>>> computer gets it's time by NTP and someone is able to change the time >>>> later on by simply plugging in some HID device.) >>>> >>> >>> To add something more: I use the system time as a bool >>> "time_was_set_once" and have choosen one day just in case something >>> needs really long to boot (e.g. because of some lengthy fsck or whatever >>> else). >>> >>> A solution to both problems might be to change the logic for hctosys >>> completly to read the time when the first RTC device appears (or when >>> the device mentioned in CONFIG_RTC_HCTOSYS_DEVICE appears). But that >>> would require a change to hctosys or the RTC subsystem, which would >>> involve more patches and discussion. As rtc-hid-sensor-time currently >>> seems to be the only RTC with the above problems, I've gone the easy >>> route and only modified this driver. >> >> Oh, damn. I've forgotten my example above with NTP. In that case setting >> the time when the first RTC appears doesn't work. > > So a general solution might be to set the system time when the first RTC > (or the one mentioned in CONFIG_RTC_HCTOSYS_DEVICE) appears AND nothing > else did set the time before. To extend that idea a bit further, I think an option timewait (similiar to rootwait) would be a nice to have. If just time wouldn't be that rare ... ;) Regards, Alexander -- 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/