From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754854Ab3DWKRz (ORCPT ); Tue, 23 Apr 2013 06:17:55 -0400 Received: from h1446028.stratoserver.net ([85.214.92.142]:41475 "EHLO mail.ahsoftware.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752005Ab3DWKRy (ORCPT ); Tue, 23 Apr 2013 06:17:54 -0400 Message-ID: <51765FB9.2050009@ahsoftware.de> Date: Tue, 23 Apr 2013 12:17:29 +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> In-Reply-To: <51765ECD.6020601@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 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. Regards, Alexander