From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CCEFAC43217 for ; Wed, 23 Feb 2022 14:26:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241550AbiBWO03 (ORCPT ); Wed, 23 Feb 2022 09:26:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42900 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236643AbiBWO02 (ORCPT ); Wed, 23 Feb 2022 09:26:28 -0500 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 32CDCB2382; Wed, 23 Feb 2022 06:26:00 -0800 (PST) Received: by verein.lst.de (Postfix, from userid 2407) id 8BB3D68AA6; Wed, 23 Feb 2022 15:25:55 +0100 (CET) Date: Wed, 23 Feb 2022 15:25:55 +0100 From: Christoph Hellwig To: Baoquan He Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, cl@linux.com, 42.hyeyoo@gmail.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz, David.Laight@aculab.com, david@redhat.com, herbert@gondor.apana.org.au, davem@davemloft.net, linux-crypto@vger.kernel.org, steffen.klassert@secunet.com, netdev@vger.kernel.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, linux-s390@vger.kernel.org, michael@walle.cc, linux-i2c@vger.kernel.org, wsa@kernel.org Subject: Re: [PATCH 1/2] dma-mapping: check dma_mask for streaming mapping allocs Message-ID: <20220223142555.GA5986@lst.de> References: <20220219005221.634-1-bhe@redhat.com> <20220219005221.634-22-bhe@redhat.com> <20220219071730.GG26711@lst.de> <20220220084044.GC93179@MiWiFi-R3L-srv> <20220222084530.GA6210@lst.de> <20220222131120.GB10093@lst.de> <20220222155904.GA13323@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 23, 2022 at 08:28:13AM +0800, Baoquan He wrote: > Could you tell more why this is wrong? According to > Documentation/core-api/dma-api.rst and DMA code, __dma_alloc_pages() is > the core function of dma_alloc_pages()/dma_alloc_noncoherent() which are > obviously streaming mapping, Why are they "obviously" streaming mappings? > why do we need to check > dev->coherent_dma_mask here? Because dev->coherent_dma_mask is the subset > of dev->dma_mask, it's safer to use dev->coherent_dma_mask in these > places? This is confusing, I talked to Hyeonggon in private mail, he has > the same feeling. Think of th coherent_dma_mask as dma_alloc_mask. It is the mask for the DMA memory allocator. dma_mask is the mask for the dma_map_* routines.