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 X-Spam-Level: X-Spam-Status: No, score=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0FB7BC00307 for ; Fri, 6 Sep 2019 12:06:38 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D2565214DE for ; Fri, 6 Sep 2019 12:06:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D2565214DE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A8D226B000A; Fri, 6 Sep 2019 08:06:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A1AE46B000C; Fri, 6 Sep 2019 08:06:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8BBAF6B000D; Fri, 6 Sep 2019 08:06:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0179.hostedemail.com [216.40.44.179]) by kanga.kvack.org (Postfix) with ESMTP id 635236B000A for ; Fri, 6 Sep 2019 08:06:35 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id EFA9E440B for ; Fri, 6 Sep 2019 12:06:34 +0000 (UTC) X-FDA: 75904368708.20.point08_5682d2be87e3b X-HE-Tag: point08_5682d2be87e3b X-Filterd-Recvd-Size: 4452 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Fri, 6 Sep 2019 12:06:34 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6CA03ABE7; Fri, 6 Sep 2019 12:06:32 +0000 (UTC) From: Nicolas Saenz Julienne To: catalin.marinas@arm.com, hch@lst.de, wahrenst@gmx.net, marc.zyngier@arm.com, robh+dt@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: f.fainelli@gmail.com, will@kernel.org, robin.murphy@arm.com, nsaenzjulienne@suse.de, linux-kernel@vger.kernel.org, mbrugger@suse.com, linux-rpi-kernel@lists.infradead.org, phill@raspberrypi.org, m.szyprowski@samsung.com Subject: [PATCH v4 4/4] mm: refresh ZONE_DMA and ZONE_DMA32 comments in 'enum zone_type' Date: Fri, 6 Sep 2019 14:06:15 +0200 Message-Id: <20190906120617.18836-5-nsaenzjulienne@suse.de> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190906120617.18836-1-nsaenzjulienne@suse.de> References: <20190906120617.18836-1-nsaenzjulienne@suse.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: These zones usage has evolved with time and the comments were outdated. This joins both ZONE_DMA and ZONE_DMA32 explanation and gives up to date examples on how they are used on different architectures. Signed-off-by: Nicolas Saenz Julienne Reviewed-by: Christoph Hellwig Reviewed-by: Catalin Marinas --- Changes in v3: - Update comment to match changes in arm64 Changes in v2: - Try another approach merging both ZONE_DMA comments into one - Address Christoph's comments - If this approach doesn't get much traction I'll just drop the patch from the series as it's not really essential include/linux/mmzone.h | 45 ++++++++++++++++++++++++------------------ 1 file changed, 26 insertions(+), 19 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 3f38c30d2f13..bf1b916c9ecb 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -357,33 +357,40 @@ struct per_cpu_nodestat { #endif /* !__GENERATING_BOUNDS.H */ =20 enum zone_type { -#ifdef CONFIG_ZONE_DMA /* - * ZONE_DMA is used when there are devices that are not able - * to do DMA to all of addressable memory (ZONE_NORMAL). Then we - * carve out the portion of memory that is needed for these devices. - * The range is arch specific. + * ZONE_DMA and ZONE_DMA32 are used when there are peripherals not able + * to DMA to all of the addressable memory (ZONE_NORMAL). + * On architectures where this area covers the whole 32 bit address + * space ZONE_DMA32 is used. ZONE_DMA is left for the ones with smaller + * DMA addressing constraints. This distinction is important as a 32bit + * DMA mask is assumed when ZONE_DMA32 is defined. Some 64-bit + * platforms may need both zones as they support peripherals with + * different DMA addressing limitations. + * + * Some examples: + * + * - i386 and x86_64 have a fixed 16M ZONE_DMA and ZONE_DMA32 for the + * rest of the lower 4G. + * + * - arm only uses ZONE_DMA, the size, up to 4G, may vary depending on + * the specific device. + * + * - arm64 has a fixed 1G ZONE_DMA and ZONE_DMA32 for the rest of the + * lower 4G. * - * Some examples + * - powerpc only uses ZONE_DMA, the size, up to 2G, may vary + * depending on the specific device. * - * Architecture Limit - * --------------------------- - * parisc, ia64, sparc <4G - * s390, powerpc <2G - * arm Various - * alpha Unlimited or 0-16MB. + * - s390 uses ZONE_DMA fixed to the lower 2G. * - * i386, x86_64 and multiple other arches - * <16M. + * - ia64 and riscv only use ZONE_DMA32. + * + * - parisc uses neither. */ +#ifdef CONFIG_ZONE_DMA ZONE_DMA, #endif #ifdef CONFIG_ZONE_DMA32 - /* - * x86_64 needs two ZONE_DMAs because it supports devices that are - * only able to do DMA to the lower 16M but also 32 bit devices that - * can only do DMA areas below 4G. - */ ZONE_DMA32, #endif /* --=20 2.23.0