Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932122AbWCGSys (ORCPT ); Tue, 7 Mar 2006 13:54:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751576AbWCGSys (ORCPT ); Tue, 7 Mar 2006 13:54:48 -0500 Received: from spirit.analogic.com ([204.178.40.4]:23822 "EHLO spirit.analogic.com") by vger.kernel.org with ESMTP id S1751559AbWCGSyq convert rfc822-to-8bit (ORCPT ); Tue, 7 Mar 2006 13:54:46 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-MimeOLE: Produced By Microsoft Exchange V6.5.7226.0 In-Reply-To: <1141756825.31814.75.camel@localhost.localdomain> x-originalarrivaltime: 07 Mar 2006 18:54:41.0300 (UTC) FILETIME=[9760F540:01C64218] Content-class: urn:content-classes:message Subject: Re: [PATCH] Document Linux's memory barriers Date: Tue, 7 Mar 2006 13:54:33 -0500 Message-ID: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [PATCH] Document Linux's memory barriers Thread-Index: AcZCGJdqnzrRo9v4R3yEUhXL6YRmOQ== References: <31492.1141753245@warthog.cambridge.redhat.com> <1141756825.31814.75.camel@localhost.localdomain> From: "linux-os \(Dick Johnson\)" To: "Alan Cox" Cc: "David Howells" , , , , , , "Linux kernel" Reply-To: "linux-os \(Dick Johnson\)" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1571 Lines: 36 On Tue, 7 Mar 2006, Alan Cox wrote: [SNIPPED...] > > Not always. MMIO ordering is outside of the CPU ordering rules and into > PCI and other bus ordering rules. Consider > > writel(STOP_DMA, &foodev->ctrl); > free_dma_buffers(foodev); > > This leads to horrible disasters. This might be a good place to document: dummy = readl(&foodev->ctrl); Will flush all pending writes to the PCI bus and that: (void) readl(&foodev->ctrl); ... won't because `gcc` may optimize it away. In fact, variable "dummy" should be global or `gcc` may make it go away as well. Cheers, Dick Johnson Penguin : Linux version 2.6.15.4 on an i686 machine (5589.50 BogoMips). Warning : 98.36% of all statistics are fiction, book release in April. _  **************************************************************** The information transmitted in this message is confidential and may be privileged. Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is prohibited. If you are not the intended recipient, please notify Analogic Corporation immediately - by replying to this message or by sending an email to DeliveryErrors@analogic.com - and destroy all copies of this information, including any attachments, without reading or disclosing them. Thank you. - 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/