Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756290AbbDJUhf (ORCPT ); Fri, 10 Apr 2015 16:37:35 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:49281 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753595AbbDJUhb (ORCPT ); Fri, 10 Apr 2015 16:37:31 -0400 Date: Fri, 10 Apr 2015 13:37:30 -0700 From: Andrew Morton To: Keerthy Cc: Igor Grinberg , , Keerthy , , , Subject: Re: [rtc-linux] [PATCH] rtc: OMAP: Add external 32k clock feature Message-Id: <20150410133730.8f84b2894efcf1bde075048f@linux-foundation.org> In-Reply-To: <5527894E.9000807@ti.com> References: <1425375722-13412-1-git-send-email-j-keerthy@ti.com> <20150324155916.cfd1b7ab442271466160283f@linux-foundation.org> <55234F25.5060708@ti.com> <5523820C.2010709@compulab.co.il> <5527894E.9000807@ti.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1599 Lines: 33 On Fri, 10 Apr 2015 13:56:54 +0530 Keerthy wrote: > >>> How do we know that all systems have this external clock and that it > >>> works OK? > >>> > >> > >> AM335 and AM43X have the external clock feature which we choose using > >> RTC_OSC_REG. I verified it works OK by seeing the RTC seconds ticking > >> even after switching the source to the external 32k Clock. > > > > AFAIU, this is related to the external (outside of SoC) oscillator, right? > > If so, there is a possibility to not assemble it on the board (at least > > on AM335) and use the internal clock source instead. > > Yes. The register 'OMAP_RTC_OSC_REG' is part of the RTC IP register set > so i assumed that it would be with the RTCs of those particular SoCs. I'm a bit lost here. AFAICT there's a risk that some manufacturers have not wired up the external oscillator, so this patch will break those systems. Do we know for sure that this cannot be the case? Is there any way in which we can get all systems working properly? If there's no way of auto-detecting an external oscillator then perhaps a module parameter is needed. If so, it would be better if the driver were to default to internal oscillator (ie: current behaviour), and the module parameter selects the external oscillator. This way, existing systems are unaffected by the kernel upgrade. -- 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/