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 32CF0C433EF for ; Thu, 24 Feb 2022 14:11:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235344AbiBXOMN (ORCPT ); Thu, 24 Feb 2022 09:12:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235348AbiBXOMI (ORCPT ); Thu, 24 Feb 2022 09:12:08 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 35C3E114E for ; Thu, 24 Feb 2022 06:11:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645711890; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QcE0EVUjCg6X/xa4J/ZeUVoMtNaV/sF9sKuaRTVThoM=; b=DsN2F64DB5SUrY+y1OVBqFXf1hUrifC5BFgVOHKhyafJMFxQHmvre7sgxsntFukvNp+Eyt lUW2t7087z0q32TmK6HP/Hncg2FvRqY9rmm+OkqQQCXjNdhOB3h1Is1HmnPlAT0MFeEgA5 8xvZoXz8hkf8i86968aqKzK/MFF3y7s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-446-1e0tpTSFOiWgY-PtsWJlVw-1; Thu, 24 Feb 2022 09:11:27 -0500 X-MC-Unique: 1e0tpTSFOiWgY-PtsWJlVw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6C8FB1006AA7; Thu, 24 Feb 2022 14:11:22 +0000 (UTC) Received: from localhost (ovpn-13-73.pek2.redhat.com [10.72.13.73]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9FC2684008; Thu, 24 Feb 2022 14:11:19 +0000 (UTC) Date: Thu, 24 Feb 2022 22:11:17 +0800 From: Baoquan He To: Christoph Hellwig Cc: 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: References: <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> <20220223142555.GA5986@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220223142555.GA5986@lst.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/23/22 at 03:25pm, Christoph Hellwig wrote: > 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? Because they are obviously not coherent mapping? With my understanding, there are two kinds of DMA mapping, coherent mapping (which is also persistent mapping), and streaming mapping. The coherent mapping will be handled during driver init, and released during driver de-init. While streaming mapping will be done when needed at any time, and released after usage. Are we going to add another kind of mapping? It's not streaming mapping, but use dev->coherent_dma_mask, just because it uses dma_alloc_xxx() api. > > > 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. I will check code further. While this may need be noted in doc, e.g dma_api.rst or dma-api-howto.rst. If you have guide, I can try to add some words to make clear this. Or leave this to people who knows this clearly. I believe it will be very helpful to understand DMA api.