From: Vineet Gupta <Vineet.Gupta1-HKixBCOQz3hWk0Htik3J/w@public.gmane.org> To: Russell King - ARM Linux <linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org> Cc: "linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Alexey Brodkin <Alexey.Brodkin-HKixBCOQz3hWk0Htik3J/w@public.gmane.org>, "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, "sparclinux-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <sparclinux-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "deanbo422-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" <deanbo422-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "hch-jcswGhMUV9g@public.gmane.org" <hch-jcswGhMUV9g@public.gmane.org>, "linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-c6x-dev-jPsnJVOj+W6hPH1hqNUYSQ@public.gmane.org" <linux-c6x-dev-jPsnJVOj+W6hPH1hqNUYSQ@public.gmane.org>, "linux-hexagon-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-hexagon-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-snps-arc-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" <linux-snps-arc-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>, "linux-xtensa-PjhNF2WwrV/0Sa2dR60CXw@public.gmane.org" <linux-xtensa-PjhNF2WwrV/0Sa2dR60CXw@public.gmane.org>, "linux-m68k-cunTk1MwBs8S/qaLPR03pWD2FQJk+8+b@public.gmane.org" <linux-m68k-cunTk1MwBs8S/qaLPR03pWD2FQJk+8+b@public.gmane.org>, "openrisc-cunTk1MwBs9a3B2Vnqf2dGD2FQJk+8+b@public.gmane.org" <openrisc-cunTk1MwBs9a3B2Vnqf2dGD2FQJk+8+b@public.gmane.org>, "green.hu-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" <green.hu-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>, "monstr-pSz03upnqPeHXe+LvDLADg@public.gmane.org" <monst> Subject: Re: dma_sync_*_for_cpu and direction=TO_DEVICE (was Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation) Date: Fri, 18 May 2018 13:35:08 -0700 [thread overview] Message-ID: <cecfe6bd-ef1f-1e25-bfcf-992d1f828efb@synopsys.com> (raw) In-Reply-To: <20180518175004.GF17671-l+eeeJia6m9URfEZ8mYm6t73F7V6hmMc@public.gmane.org> On 05/18/2018 10:50 AM, Russell King - ARM Linux wrote: > On Fri, May 18, 2018 at 10:20:02AM -0700, Vineet Gupta wrote: >> I never understood the need for this direction. And if memory serves me >> right, at that time I was seeing twice the amount of cache flushing ! > It's necessary. Take a moment to think carefully about this: > > dma_map_single(, dir) > > dma_sync_single_for_cpu(, dir) > > dma_sync_single_for_device(, dir) > > dma_unmap_single(, dir) As an aside, do these imply a state machine of sorts - does a driver needs to always call map_single first ? My original point of contention/confusion is the specific combinations of API and direction, specifically for_cpu(TO_DEV) and for_device(TO_CPU) Semantically what does dma_sync_single_for_cpu(TO_DEV) even imply for a non dma coherent arch. Your tables below have "none" for both, implying it is unlikely to be a real combination (for ARM and ARC atleast). The other case, actually @dir TO_CPU, independent of for_{cpu, device} implies driver intends to touch it after the call, so it would invalidate any stray lines, unconditionally (and not just for speculative prefetch case). > In the case of a DMA-incoherent architecture, the operations done at each > stage depend on the direction argument: > > map for_cpu for_device unmap > TO_DEV writeback none writeback none > TO_CPU invalidate invalidate* invalidate invalidate* > BIDIR writeback invalidate writeback invalidate > > * - only necessary if the CPU speculatively prefetches. > > The multiple invalidations for the TO_CPU case handles different > conditions that can result in data corruption, and for some CPUs, all > four are necessary. Can you please explain in some more detail, TO_CPU row, why invalidate is conditional sometimes. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
WARNING: multiple messages have this Message-ID (diff)
From: Vineet Gupta <Vineet.Gupta1@synopsys.com> To: Russell King - ARM Linux <linux@armlinux.org.uk> Cc: Alexey Brodkin <Alexey.Brodkin@synopsys.com>, "hch@lst.de" <hch@lst.de>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-xtensa@linux-xtensa.org" <linux-xtensa@linux-xtensa.org>, "monstr@monstr.eu" <monstr@monstr.eu>, "deanbo422@gmail.com" <deanbo422@gmail.com>, "linux-c6x-dev@linux-c6x.org" <linux-c6x-dev@linux-c6x.org>, "linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>, "linux-sh@vger.kernel.org" <linux-sh@vger.kernel.org>, "linux-m68k@lists.linux-m68k.org" <linux-m68k@lists.linux-m68k.org>, "linux-hexagon@vger.kernel.org" <linux-hexagon@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>, "openrisc@lists.librecores.org" <openrisc@lists.librecores.org>, "green.hu@gmail.com" <green.hu@gmail.com>, "linux-alpha@vger.kernel.org" <linux-alpha@vger.kernel.org>, "sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>, "nios2-dev@lists.rocketboards.org" <nios2-dev@lists.rocketboards.org>, Andrew Morton <akpm@linux-foundation.org>, "linux-snps-arc@lists.infradead.org" <linux-snps-arc@lists.infradead.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org> Subject: Re: dma_sync_*_for_cpu and direction=TO_DEVICE (was Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation) Date: Fri, 18 May 2018 13:35:08 -0700 [thread overview] Message-ID: <cecfe6bd-ef1f-1e25-bfcf-992d1f828efb@synopsys.com> (raw) Message-ID: <20180518203508.JT0jkyWHE9Q9-gNUEgz9nsaUjYwQf8tLo0XsBeNi99A@z> (raw) In-Reply-To: <20180518175004.GF17671@n2100.armlinux.org.uk> On 05/18/2018 10:50 AM, Russell King - ARM Linux wrote: > On Fri, May 18, 2018 at 10:20:02AM -0700, Vineet Gupta wrote: >> I never understood the need for this direction. And if memory serves me >> right, at that time I was seeing twice the amount of cache flushing ! > It's necessary. Take a moment to think carefully about this: > > dma_map_single(, dir) > > dma_sync_single_for_cpu(, dir) > > dma_sync_single_for_device(, dir) > > dma_unmap_single(, dir) As an aside, do these imply a state machine of sorts - does a driver needs to always call map_single first ? My original point of contention/confusion is the specific combinations of API and direction, specifically for_cpu(TO_DEV) and for_device(TO_CPU) Semantically what does dma_sync_single_for_cpu(TO_DEV) even imply for a non dma coherent arch. Your tables below have "none" for both, implying it is unlikely to be a real combination (for ARM and ARC atleast). The other case, actually @dir TO_CPU, independent of for_{cpu, device} implies driver intends to touch it after the call, so it would invalidate any stray lines, unconditionally (and not just for speculative prefetch case). > In the case of a DMA-incoherent architecture, the operations done at each > stage depend on the direction argument: > > map for_cpu for_device unmap > TO_DEV writeback none writeback none > TO_CPU invalidate invalidate* invalidate invalidate* > BIDIR writeback invalidate writeback invalidate > > * - only necessary if the CPU speculatively prefetches. > > The multiple invalidations for the TO_CPU case handles different > conditions that can result in data corruption, and for some CPUs, all > four are necessary. Can you please explain in some more detail, TO_CPU row, why invalidate is conditional sometimes.
next prev parent reply other threads:[~2018-05-18 20:35 UTC|newest] Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-11 7:59 common non-cache coherent direct dma mapping ops Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 01/20] dma-mapping: simplify Kconfig dependencies Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig [not found] ` <20180511075945.16548-1-hch-jcswGhMUV9g@public.gmane.org> 2018-05-11 7:59 ` [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig [not found] ` <20180511075945.16548-3-hch-jcswGhMUV9g@public.gmane.org> 2018-05-18 13:03 ` Alexey Brodkin 2018-05-18 13:03 ` Alexey Brodkin [not found] ` <bad125dff49f6e49c895e818c9d1abb346a46e8e.camel-HKixBCOQz3hWk0Htik3J/w@public.gmane.org> 2018-05-18 13:27 ` hch-jcswGhMUV9g 2018-05-18 13:27 ` hch [not found] ` <20180518132731.GA31125-jcswGhMUV9g@public.gmane.org> 2018-05-18 14:13 ` Alexey Brodkin 2018-05-18 14:13 ` Alexey Brodkin 2018-05-18 17:28 ` Vineet Gupta 2018-05-18 17:28 ` Vineet Gupta 2018-05-18 17:20 ` dma_sync_*_for_cpu and direction=TO_DEVICE (was Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation) Vineet Gupta 2018-05-18 17:20 ` Vineet Gupta 2018-05-18 17:50 ` Russell King - ARM Linux 2018-05-18 17:50 ` Russell King - ARM Linux [not found] ` <20180518175004.GF17671-l+eeeJia6m9URfEZ8mYm6t73F7V6hmMc@public.gmane.org> 2018-05-18 19:57 ` Alexey Brodkin 2018-05-18 19:57 ` Alexey Brodkin [not found] ` <182840dedb4890a88c672b1c5d556920bf89a8fb.camel-HKixBCOQz3hWk0Htik3J/w@public.gmane.org> 2018-05-18 21:33 ` Russell King - ARM Linux 2018-05-18 21:33 ` Russell King - ARM Linux 2018-05-18 20:35 ` Vineet Gupta [this message] 2018-05-18 20:35 ` Vineet Gupta 2018-05-18 21:55 ` Russell King - ARM Linux 2018-05-18 21:55 ` Russell King - ARM Linux 2018-05-18 20:05 ` [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation Helge Deller 2018-05-18 20:05 ` Helge Deller [not found] ` <0c5d27e9-2799-eb38-8b09-47a04c48b5c7-Mmb7MZpHnFY@public.gmane.org> 2018-05-19 6:38 ` hch-jcswGhMUV9g 2018-05-19 6:38 ` hch 2018-05-11 7:59 ` [PATCH 03/20] arc: use generic dma_noncoherent_ops Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig [not found] ` <20180511075945.16548-4-hch-jcswGhMUV9g@public.gmane.org> 2018-05-11 12:44 ` Alexey Brodkin 2018-05-11 12:44 ` Alexey Brodkin 2018-05-11 7:59 ` [PATCH 04/20] arm-nommu: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig [not found] ` <20180511075945.16548-5-hch-jcswGhMUV9g@public.gmane.org> 2018-05-11 9:11 ` Russell King - ARM Linux 2018-05-11 9:11 ` Russell King - ARM Linux [not found] ` <20180511091114.GA16141-l+eeeJia6m9URfEZ8mYm6t73F7V6hmMc@public.gmane.org> 2018-05-22 11:53 ` Christoph Hellwig 2018-05-22 11:53 ` Christoph Hellwig 2018-05-11 13:56 ` John Garry 2018-05-11 13:56 ` John Garry 2018-05-11 7:59 ` [PATCH 05/20] c6x: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig [not found] ` <20180511075945.16548-6-hch-jcswGhMUV9g@public.gmane.org> 2018-05-15 0:25 ` [Linux-c6x-dev] " Mark Salter 2018-05-15 0:25 ` Mark Salter 2018-05-11 7:59 ` [PATCH 06/20] hexagon: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 07/20] m68k: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 08/20] microblaze: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 09/20] microblaze: remove the consistent_sync and consistent_sync_page Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 10/20] nds32: use generic dma_noncoherent_ops Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 11/20] nios2: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 12/20] openrisc: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 13/20] sh: simplify get_arch_dma_ops Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 14/20] sh: introduce a sh_cacheop_vaddr helper Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 15/20] sh: use dma_direct_ops for the CONFIG_DMA_COHERENT case Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 16/20] mm: split arch/sh/mm/consistent.c Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 17/20] sh: use generic dma_noncoherent_ops Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 18/20] xtensa: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 19/20] sparc: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-11 7:59 ` [PATCH 20/20] parisc: " Christoph Hellwig 2018-05-11 7:59 ` Christoph Hellwig 2018-05-13 13:26 ` common non-cache coherent direct dma mapping ops Helge Deller 2018-05-13 13:26 ` Helge Deller
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