From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sinan Kaya Subject: Re: [PATCH] ia64: fix barrier placement for write* / dma mapping Date: Wed, 1 Aug 2018 01:00:32 -0700 Message-ID: <6ac80566-be1b-3dfc-e6b7-3c38131673ef@kernel.org> References: <20180731172031.4447-1-hch@lst.de> <20180731172031.4447-2-hch@lst.de> <20180801072947.GD20224@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180801072947.GD20224@lst.de> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig , okaya@codeaurora.org Cc: Tony Luck , Fenghua Yu , Arnd Bergmann , linux-ia64@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org List-Id: iommu@lists.linux-foundation.org On 8/1/2018 12:29 AM, Christoph Hellwig wrote: >> I asked this question to Tony Luck before. If I remember right, >> his answer was: >> >> CPU guarantees outstanding writes to be flushed when a register write >> instruction is executed and an additional barrier instruction is not >> needed. > That would be great. It still doesn't explain the barriers in the > dma sync routines. Those have been there since the following commit > in the history tree: Yeah, I'll let Tony confirm my understanding.