From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH 5/8] arm64: use ZONE_DMA on DMA addressing limited devices Date: Wed, 31 Jul 2019 18:07:42 +0100 Message-ID: <20190731170742.GC17773@arrakis.emea.arm.com> References: <20190731154752.16557-1-nsaenzjulienne@suse.de> <20190731154752.16557-6-nsaenzjulienne@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190731154752.16557-6-nsaenzjulienne@suse.de> Sender: linux-kernel-owner@vger.kernel.org To: Nicolas Saenz Julienne Cc: hch@lst.de, wahrenst@gmx.net, marc.zyngier@arm.com, Robin Murphy , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, iommu@lists.linux-foundation.org, linux-mm@kvack.org, Will Deacon , phill@raspberryi.org, f.fainelli@gmail.com, linux-kernel@vger.kernel.org, robh+dt@kernel.org, eric@anholt.net, mbrugger@suse.com, akpm@linux-foundation.org, frowand.list@gmail.com, m.szyprowski@samsung.com, linux-rpi-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org On Wed, Jul 31, 2019 at 05:47:48PM +0200, Nicolas Saenz Julienne wrote: > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index 1c4ffabbe1cb..f5279ef85756 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -50,6 +50,13 @@ > s64 memstart_addr __ro_after_init = -1; > EXPORT_SYMBOL(memstart_addr); > > +/* > + * We might create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA is needed if there > + * are periferals unable to address the first naturally aligned 4GB of ram. > + * ZONE_DMA32 will be expanded to cover the rest of that memory. If such > + * limitations doesn't exist only ZONE_DMA32 is created. > + */ Shouldn't we instead only create ZONE_DMA to cover the whole 32-bit range and leave ZONE_DMA32 empty? Can__GFP_DMA allocations fall back onto ZONE_DMA32? -- Catalin