From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vineet Gupta 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 Message-ID: References: <20180511075945.16548-1-hch@lst.de> <20180511075945.16548-3-hch@lst.de> <5ac5b1e3-9b96-9c7c-4dfe-f65be45ec179@synopsys.com> <20180518175004.GF17671@n2100.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; Format="flowed" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <20180518175004.GF17671-l+eeeJia6m9URfEZ8mYm6t73F7V6hmMc@public.gmane.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Russell King - ARM Linux Cc: "linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Alexey Brodkin , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , "sparclinux-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "deanbo422-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" , "hch-jcswGhMUV9g@public.gmane.org" , "linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-c6x-dev-jPsnJVOj+W6hPH1hqNUYSQ@public.gmane.org" , "linux-hexagon-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-snps-arc-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-xtensa-PjhNF2WwrV/0Sa2dR60CXw@public.gmane.org" , "linux-m68k-cunTk1MwBs8S/qaLPR03pWD2FQJk+8+b@public.gmane.org" , "openrisc-cunTk1MwBs9a3B2Vnqf2dGD2FQJk+8+b@public.gmane.org" , "green.hu-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "monstr-pSz03upnqPeHXe+LvDLADg@public.gmane.org" List-Id: linux-arch.vger.kernel.org T24gMDUvMTgvMjAxOCAxMDo1MCBBTSwgUnVzc2VsbCBLaW5nIC0gQVJNIExpbnV4IHdyb3RlOgo+ IE9uIEZyaSwgTWF5IDE4LCAyMDE4IGF0IDEwOjIwOjAyQU0gLTA3MDAsIFZpbmVldCBHdXB0YSB3 cm90ZToKPj4gSSBuZXZlciB1bmRlcnN0b29kIHRoZSBuZWVkIGZvciB0aGlzIGRpcmVjdGlvbi4g QW5kIGlmIG1lbW9yeSBzZXJ2ZXMgbWUKPj4gcmlnaHQsIGF0IHRoYXQgdGltZSBJIHdhcyBzZWVp bmcgdHdpY2UgdGhlIGFtb3VudCBvZiBjYWNoZSBmbHVzaGluZyAhCj4gSXQncyBuZWNlc3Nhcnku ICBUYWtlIGEgbW9tZW50IHRvIHRoaW5rIGNhcmVmdWxseSBhYm91dCB0aGlzOgo+Cj4gCWRtYV9t YXBfc2luZ2xlKCwgZGlyKQo+Cj4gCWRtYV9zeW5jX3NpbmdsZV9mb3JfY3B1KCwgZGlyKQo+Cj4g CWRtYV9zeW5jX3NpbmdsZV9mb3JfZGV2aWNlKCwgZGlyKQo+Cj4gCWRtYV91bm1hcF9zaW5nbGUo LCBkaXIpCgpBcyBhbiBhc2lkZSwgZG8gdGhlc2UgaW1wbHkgYSBzdGF0ZSBtYWNoaW5lIG9mIHNv cnRzIC0gZG9lcyBhIGRyaXZlciBuZWVkcyB0byAKYWx3YXlzIGNhbGwgbWFwX3NpbmdsZSBmaXJz dCA/CgpNeSBvcmlnaW5hbCBwb2ludCBvZiBjb250ZW50aW9uL2NvbmZ1c2lvbiBpcyB0aGUgc3Bl Y2lmaWMgY29tYmluYXRpb25zIG9mIEFQSSBhbmQgCmRpcmVjdGlvbiwgc3BlY2lmaWNhbGx5IGZv cl9jcHUoVE9fREVWKSBhbmQgZm9yX2RldmljZShUT19DUFUpCgpTZW1hbnRpY2FsbHkgd2hhdCBk b2VzIGRtYV9zeW5jX3NpbmdsZV9mb3JfY3B1KFRPX0RFVikgZXZlbiBpbXBseSBmb3IgYSBub24g ZG1hIApjb2hlcmVudCBhcmNoLgpZb3VyIHRhYmxlcyBiZWxvdyBoYXZlICJub25lIiBmb3IgYm90 aCwgaW1wbHlpbmcgaXQgaXMgdW5saWtlbHkgdG8gYmUgYSByZWFsIApjb21iaW5hdGlvbiAoZm9y IEFSTSBhbmQgQVJDIGF0bGVhc3QpLgoKVGhlIG90aGVyIGNhc2UsIGFjdHVhbGx5IEBkaXIgVE9f Q1BVLCBpbmRlcGVuZGVudCBvZiBmb3Jfe2NwdSwgZGV2aWNlfcKgIGltcGxpZXMgCmRyaXZlciBp bnRlbmRzIHRvIHRvdWNoIGl0IGFmdGVyIHRoZSBjYWxsLCBzbyBpdCB3b3VsZCBpbnZhbGlkYXRl IGFueSBzdHJheSBsaW5lcywgCnVuY29uZGl0aW9uYWxseSAoYW5kIG5vdCBqdXN0IGZvciBzcGVj dWxhdGl2ZSBwcmVmZXRjaCBjYXNlKS4KCgo+IEluIHRoZSBjYXNlIG9mIGEgRE1BLWluY29oZXJl bnQgYXJjaGl0ZWN0dXJlLCB0aGUgb3BlcmF0aW9ucyBkb25lIGF0IGVhY2gKPiBzdGFnZSBkZXBl bmQgb24gdGhlIGRpcmVjdGlvbiBhcmd1bWVudDoKPgo+IAltYXAJCWZvcl9jcHUJCWZvcl9kZXZp Y2UJdW5tYXAKPiBUT19ERVYJd3JpdGViYWNrCW5vbmUJCXdyaXRlYmFjawlub25lCj4gVE9fQ1BV CWludmFsaWRhdGUJaW52YWxpZGF0ZSoJaW52YWxpZGF0ZQlpbnZhbGlkYXRlKgo+IEJJRElSCXdy aXRlYmFjawlpbnZhbGlkYXRlCXdyaXRlYmFjawlpbnZhbGlkYXRlCj4KPiAqIC0gb25seSBuZWNl c3NhcnkgaWYgdGhlIENQVSBzcGVjdWxhdGl2ZWx5IHByZWZldGNoZXMuCj4KPiBUaGUgbXVsdGlw bGUgaW52YWxpZGF0aW9ucyBmb3IgdGhlIFRPX0NQVSBjYXNlIGhhbmRsZXMgZGlmZmVyZW50Cj4g Y29uZGl0aW9ucyB0aGF0IGNhbiByZXN1bHQgaW4gZGF0YSBjb3JydXB0aW9uLCBhbmQgZm9yIHNv bWUgQ1BVcywgYWxsCj4gZm91ciBhcmUgbmVjZXNzYXJ5LgoKQ2FuIHlvdSBwbGVhc2UgZXhwbGFp biBpbiBzb21lIG1vcmUgZGV0YWlsLCBUT19DUFUgcm93LCB3aHkgaW52YWxpZGF0ZSBpcyAKY29u ZGl0aW9uYWwgc29tZXRpbWVzLgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fXwppb21tdSBtYWlsaW5nIGxpc3QKaW9tbXVAbGlzdHMubGludXgtZm91bmRhdGlv bi5vcmcKaHR0cHM6Ly9saXN0cy5saW51eGZvdW5kYXRpb24ub3JnL21haWxtYW4vbGlzdGluZm8v aW9tbXU= From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtprelay6.synopsys.com ([198.182.37.59]:59177 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751952AbeERUfY (ORCPT ); Fri, 18 May 2018 16:35:24 -0400 Subject: Re: dma_sync_*_for_cpu and direction=TO_DEVICE (was Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation) References: <20180511075945.16548-1-hch@lst.de> <20180511075945.16548-3-hch@lst.de> <5ac5b1e3-9b96-9c7c-4dfe-f65be45ec179@synopsys.com> <20180518175004.GF17671@n2100.armlinux.org.uk> From: Vineet Gupta Message-ID: Date: Fri, 18 May 2018 13:35:08 -0700 MIME-Version: 1.0 In-Reply-To: <20180518175004.GF17671@n2100.armlinux.org.uk> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org List-ID: To: Russell King - ARM Linux Cc: Alexey Brodkin , "hch@lst.de" , "linux-arch@vger.kernel.org" , "linux-xtensa@linux-xtensa.org" , "monstr@monstr.eu" , "deanbo422@gmail.com" , "linux-c6x-dev@linux-c6x.org" , "linux-parisc@vger.kernel.org" , "linux-sh@vger.kernel.org" , "linux-m68k@lists.linux-m68k.org" , "linux-hexagon@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "iommu@lists.linux-foundation.org" , "openrisc@lists.librecores.org" , "green.hu@gmail.com" , "linux-alpha@vger.kernel.org" , "sparclinux@vger.kernel.org" , "nios2-dev@lists.rocketboards.org" , Andrew Morton , "linux-snps-arc@lists.infradead.org" , "linux-arm-kernel@lists.infradead.org" Message-ID: <20180518203508.JT0jkyWHE9Q9-gNUEgz9nsaUjYwQf8tLo0XsBeNi99A@z> 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.