Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754919Ab3JXLAk (ORCPT ); Thu, 24 Oct 2013 07:00:40 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:60720 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754517Ab3JXLAj (ORCPT ); Thu, 24 Oct 2013 07:00:39 -0400 X-IronPort-AV: E=Sophos;i="4.93,561,1378857600"; d="scan'208";a="64236332" Date: Thu, 24 Oct 2013 11:44:50 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Konrad Rzeszutek Wilk CC: Stefano Stabellini , , , , Subject: Re: [PATCH v8 13/19] swiotlb-xen: use xen_dma_map/unmap_page, xen_dma_sync_single_for_cpu/device In-Reply-To: <20131023195154.GB28963@phenom.dumpdata.com> Message-ID: References: <1382031814-8782-13-git-send-email-stefano.stabellini@eu.citrix.com> <20131023140927.GD27771@phenom.dumpdata.com> <20131023195154.GB28963@phenom.dumpdata.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1796 Lines: 43 On Wed, 23 Oct 2013, Konrad Rzeszutek Wilk wrote: > On Wed, Oct 23, 2013 at 06:20:25PM +0100, Stefano Stabellini wrote: > > On Wed, 23 Oct 2013, Konrad Rzeszutek Wilk wrote: > > > On Thu, Oct 17, 2013 at 06:43:28PM +0100, Stefano Stabellini wrote: > > > > Call xen_dma_map_page, xen_dma_unmap_page, xen_dma_sync_single_for_cpu, > > > > xen_dma_sync_single_for_device from swiotlb-xen to ensure cpu/device > > > > coherency of the pages used for DMA, including the ones belonging to the > > > > swiotlb buffer. > > > > > > You lost me. > > > > > > Isn't it the driver's responsibility to do this? > > > > > > Looking at what 'xen_dma_map_page()' does for x86 it looks to add an extra > > > call - page_to_phys - and we ignore it here. > > > > map_page on arm calls the right cache flushes needed to communicate with > > the device. Same with unmap_page. > > If this is flushing the cache then I think it makes more sense to do > that without this fancy 'dma_map_page'. > > Just call it 'xen_flush_dma_page' and make it a nop on all platforms > except ARM. I am OK with making it a nop on x86, it makes sense. However I would like to keep it called xen_dma_map_page: after all it corresponds exactly to the native map_page dma_op. It is part of the same "contract". > > On x86 they are basically nop. > > It calls page_to_phys in your patch. That is hardly nop. I see. It is certainly worth optimizing it out on x86. Of course if one day the x86 map_page dma_op starts doing something useful, we can go back to call it from xen_dma_map_page. -- 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/