From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932511AbWGZAh5 (ORCPT ); Tue, 25 Jul 2006 20:37:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932512AbWGZAh5 (ORCPT ); Tue, 25 Jul 2006 20:37:57 -0400 Received: from terminus.zytor.com ([192.83.249.54]:53416 "EHLO terminus.zytor.com") by vger.kernel.org with ESMTP id S932511AbWGZAh4 (ORCPT ); Tue, 25 Jul 2006 20:37:56 -0400 Message-ID: <44C6B925.8040606@zytor.com> Date: Tue, 25 Jul 2006 17:36:53 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 1.5.0.4 (X11/20060614) MIME-Version: 1.0 To: Neil Horman CC: Segher Boessenkool , Dave Airlie , linux-kernel@vger.kernel.org, a.zummo@towertech.it, jg@freedesktop.org Subject: Re: [PATCH] RTC: Add mmap method to rtc character driver References: <20060725194733.GJ4608@hmsreliant.homelinux.net> <21d7e9970607251304n5681bf44gc751c21fd79be99d@mail.gmail.com> <44C67E1A.7050105@zytor.com> <20060725204736.GK4608@hmsreliant.homelinux.net> <44C6842C.8020501@zytor.com> <20060725222547.GA3973@localhost.localdomain> <70FED39F-E2DF-48C8-B401-97F8813B988E@kernel.crashing.org> <20060725235644.GA5147@localhost.localdomain> <44C6B117.80300@zytor.com> <20060726002043.GA5192@localhost.localdomain> In-Reply-To: <20060726002043.GA5192@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Neil Horman wrote: >>>> >>> It there any arch for which the rtc driver doesn't function? >> Yes, there are plenty of systems which don't have an RTC, or have an RTC >> which can't generate interrupts. >> > Ok, for those implementations which don't have an RTC that the rtc driver can > drive, the mmap functionality will not work, but at that point what interface > are you left with at all for obtaining periodic time? Depends completely on the hardware. Some hardware will rely on cycle counters, some may rely on I/O devices which may or may not be mappable into user space, and some will have to enter the kernel. These aren't compatible with your programming model. -hpa