From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752376Ab1LHNJS (ORCPT ); Thu, 8 Dec 2011 08:09:18 -0500 Received: from h5.dl5rb.org.uk ([81.2.74.5]:43265 "EHLO linux-mips.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751266Ab1LHNJR (ORCPT ); Thu, 8 Dec 2011 08:09:17 -0500 Date: Thu, 8 Dec 2011 13:08:35 +0000 From: Ralf Baechle To: zhzhl555@gmail.com Cc: a.zummo@towertech.it, rtc-linux@googlegroups.com, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, keguang.zhang@gmail.com, wuzhangjin@gmail.com, r0bertz@gentoo.org Subject: Re: [PATCH] MIPS: Add RTC support for loongson1B Message-ID: <20111208130835.GC10113@linux-mips.org> References: <1322729078-6141-1-git-send-email-zhzhl555@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1322729078-6141-1-git-send-email-zhzhl555@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 01, 2011 at 04:44:38PM +0800, zhzhl555@gmail.com wrote: > + writel(t, SYS_TOYWRITE1); > + __asm__ volatile ("sync"); > + c = 0x10000; > + while ((readl(SYS_COUNTER_CNTRL) & SYS_CNTRL_TS) && --c) > + usleep_range(1000, 3000); Why the SYNC instruction? This is an uncached write and on all MIPS CPUs the SYNC instruction will only make sure the write has left the CPU's write buffers. There is no guarantee that by the time the SYNC has completed the write has actually reached its destination. If that is what you want, read something from device. Reads will only complete after all preceeding writes have completed. In this driver all instances of SYNC instructions are followed by polling loops reading from the RTC which means all SYNCs should be unnecessary. Or? Ralf