From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756589AbbKEF5g (ORCPT ); Thu, 5 Nov 2015 00:57:36 -0500 Received: from relay1.mentorg.com ([192.94.38.131]:64868 "EHLO relay1.mentorg.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756364AbbKEF5e convert rfc822-to-8bit (ORCPT ); Thu, 5 Nov 2015 00:57:34 -0500 From: "Sharma, Sanjeev" To: Russell King - ARM Linux , Will Deacon CC: "m.szyprowski@samsung.com" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] ARM:dma-mapping: Handle DMA_BIDIRECTIONAL in _dma_page_cpu_to_dev() Thread-Topic: [PATCH] ARM:dma-mapping: Handle DMA_BIDIRECTIONAL in _dma_page_cpu_to_dev() Thread-Index: AQHRFuclJPAemyM/HkGrutuyZj2Y+J6LrEmAgAAEOQCAATrcQA== Date: Thu, 5 Nov 2015 05:56:10 +0000 Message-ID: References: <1446631008-5854-1-git-send-email-sanjeev_sharma@mentor.com> <20151104103913.GC5405@arm.com> <20151104105420.GL8644@n2100.arm.linux.org.uk> In-Reply-To: <20151104105420.GL8644@n2100.arm.linux.org.uk> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [137.202.0.76] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org -----Original Message----- From: Russell King - ARM Linux [mailto:linux@arm.linux.org.uk] Sent: Wednesday, November 04, 2015 4:24 PM To: Will Deacon Cc: Sharma, Sanjeev; m.szyprowski@samsung.com; linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org Subject: Re: [PATCH] ARM:dma-mapping: Handle DMA_BIDIRECTIONAL in _dma_page_cpu_to_dev() On Wed, Nov 04, 2015 at 10:39:13AM +0000, Will Deacon wrote: > On Wed, Nov 04, 2015 at 03:26:48PM +0530, Sanjeev Sharma wrote: > > _dma_page_cpu_to_dev() treat DMA_BIDIRECTIONAL similar to > > DMA_TO_DEVICE which means that destination buffer is device > > memory,means cpu may have written some data to source buffer and > > data may be in cache line.For cleaner operation we need to call > > outer_flush_range() which will clean and invalidate outer cache lines. > > Why isn't the clean sufficient in this case? We're mapping the buffer > to the device, so we clean the dirty lines in the CPU caches and make > them visible to the device. If the CPU later wants to read the buffer > (i.e. after the device has DMA'd into it), you'll need to map the > buffer to the CPU, which will perform the invalidation of the CPU caches. Indeed. bidirectional mode is already handled prefectly well by this code. No patches are required. Thanks Russell & Will for providing input. Let's assume , CPU don't read the buffer then there could be the problem correct ? IMO, to handle every use case outer_flush_range can be used ? If still it doesn't make sense to use flush on bidirectional mappings, then FIXME comment should be removed from the function to avoid any Confusion. (I never received the original email.) -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.