From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from fed1rmmtao08.cox.net (fed1rmmtao08.cox.net [68.230.241.31]) by ozlabs.org (Postfix) with ESMTP id 0232967A45 for ; Wed, 19 Jan 2005 05:33:40 +1100 (EST) Date: Tue, 18 Jan 2005 11:33:37 -0700 From: Tom Rini To: Tolunay Orkun Message-ID: <20050118183337.GK28724@smtp.west.cox.net> References: <41EC29A8.1040703@mvista.com> <20050118161515.GI28724@smtp.west.cox.net> <93780AB0-696D-11D9-81BE-003065F9B7DC@embeddededge.com> <41ED49E2.5050401@orkun.us> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <41ED49E2.5050401@orkun.us> Cc: linuxppc-dev@ozlabs.org Subject: Re: [RFC] Option to disable mapping genrtc calls to ppc_md calls List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Jan 18, 2005 at 11:39:46AM -0600, Tolunay Orkun wrote: > Dan Malek wrote: > > > >On Jan 18, 2005, at 11:15 AM, Tom Rini wrote: > > > >>On Mon, Jan 17, 2005 at 02:10:00PM -0700, Mark A. Greer wrote: > > > > > >>>There are 2 reasons to not use the ppc_md.get_rtc_time() et. al. > >>>interfaces: > >>>1) They are called before the i2c driver is initialized and even loaded > >>>if its a module. > > > > > >There are three reasons. You don't want to use an I2c rtc clock at > >all in these functions because they get can get called from the > >clock interrupt to update the time in the rtc. If it does happen to work, > >it creates long latencies in the timer interrupt. If the i2c requires an > >interrupt, they system will crash or hang. > > > >A system using an I2C RTC should find some way to access the > >clock from application space as a standard I2C device and manage > >time/clock from the application, not from the kernel. > > This is exactly what I've done for our PPC405GP based Linux port > (2.4.25). I've written a clone of hwclock utility using /dev/i2c0 to > access Dallas RTC chip with I2C interface. I setthe system clock from > RTC within /etc/rcS (Busybox). It is less than perfect as early logs > have the date wrong but it was the direction of least resistance. > > Still, I think there should be a better standardized RTC interface to > help deal with I2C/SMBus based RTC chips. There kind of is now, arch/arm/common/rtctime.c (thought of for I2C RTCs and has alarm support). -- Tom Rini http://gate.crashing.org/~trini/