From: Robin Murphy <robin.murphy@arm.com> To: Christoph Hellwig <hch@lst.de>, Chao Gao <chao.gao@intel.com> Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, m.szyprowski@samsung.com, Wang Zhaoyang1 <zhaoyang1.wang@intel.com>, Gao Liang <liang.gao@intel.com>, Kevin Tian <kevin.tian@intel.com> Subject: Re: [PATCH] dma-direct: avoid redundant memory sync for swiotlb Date: Wed, 13 Apr 2022 14:10:56 +0100 [thread overview] Message-ID: <4a993382-6a29-a0f4-4600-90ab60ad982a@arm.com> (raw) In-Reply-To: <20220413045958.GA31209@lst.de> On 2022-04-13 05:59, Christoph Hellwig wrote: > On Wed, Apr 13, 2022 at 09:02:02AM +0800, Chao Gao wrote: >> dma_direct_sync_single_for_cpu() also calls arch_sync_dma_for_cpu_all() >> and arch_dma_mark_clean() in some cases. if SWIOTLB does sync internally, >> should these two functions be called by SWIOTLB? >> >> Personally, it might be better if swiotlb can just focus on bounce buffer >> alloc/free. Adding more DMA coherence logic into swiotlb will make it >> a little complicated. >> >> How about an open-coded version of dma_direct_sync_single_for_cpu >> in dma_direct_unmap_page with swiotlb_sync_single_for_cpu replaced by >> swiotlb_tbl_unmap_single? > > I don't think the swiotlb and non-coherent case ever fully worked. > Before the merge of swiotlb into dma-direct they obviously were > mutally exclusive, and even now all the cache maintainance is done > on the physical address of the original data, not the swiotlb buffer. Are you sure? AFAICS swiotlb_map() does the right thing, and dma_direct_{sync,unmap} are working off the DMA address, which is that of the bounce slot when SWIOTLB is involved (not least, how would the is_swiotlb_buffer() checks work otherwise?) > If we want to fix that properly all the arch dma calls will need to > move into swiotlb, but that is a much bigger patch. > > So for now I'd be happy with the one liner presented here, but > eventually the whole area could use an overhaul. Sure, whoever gets round to tackling DMA_ATTR_NO_SNOOP first will need to go through all the cache maintenance hooks anyway, so happy to kick the can down the road until then. Thanks, Robin.
WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy@arm.com> To: Christoph Hellwig <hch@lst.de>, Chao Gao <chao.gao@intel.com> Cc: Kevin Tian <kevin.tian@intel.com>, Wang Zhaoyang1 <zhaoyang1.wang@intel.com>, linux-kernel@vger.kernel.org, Gao Liang <liang.gao@intel.com>, iommu@lists.linux-foundation.org Subject: Re: [PATCH] dma-direct: avoid redundant memory sync for swiotlb Date: Wed, 13 Apr 2022 14:10:56 +0100 [thread overview] Message-ID: <4a993382-6a29-a0f4-4600-90ab60ad982a@arm.com> (raw) In-Reply-To: <20220413045958.GA31209@lst.de> On 2022-04-13 05:59, Christoph Hellwig wrote: > On Wed, Apr 13, 2022 at 09:02:02AM +0800, Chao Gao wrote: >> dma_direct_sync_single_for_cpu() also calls arch_sync_dma_for_cpu_all() >> and arch_dma_mark_clean() in some cases. if SWIOTLB does sync internally, >> should these two functions be called by SWIOTLB? >> >> Personally, it might be better if swiotlb can just focus on bounce buffer >> alloc/free. Adding more DMA coherence logic into swiotlb will make it >> a little complicated. >> >> How about an open-coded version of dma_direct_sync_single_for_cpu >> in dma_direct_unmap_page with swiotlb_sync_single_for_cpu replaced by >> swiotlb_tbl_unmap_single? > > I don't think the swiotlb and non-coherent case ever fully worked. > Before the merge of swiotlb into dma-direct they obviously were > mutally exclusive, and even now all the cache maintainance is done > on the physical address of the original data, not the swiotlb buffer. Are you sure? AFAICS swiotlb_map() does the right thing, and dma_direct_{sync,unmap} are working off the DMA address, which is that of the bounce slot when SWIOTLB is involved (not least, how would the is_swiotlb_buffer() checks work otherwise?) > If we want to fix that properly all the arch dma calls will need to > move into swiotlb, but that is a much bigger patch. > > So for now I'd be happy with the one liner presented here, but > eventually the whole area could use an overhaul. Sure, whoever gets round to tackling DMA_ATTR_NO_SNOOP first will need to go through all the cache maintenance hooks anyway, so happy to kick the can down the road until then. Thanks, Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2022-04-13 13:11 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-12 11:38 [PATCH] dma-direct: avoid redundant memory sync for swiotlb Chao Gao 2022-04-12 11:38 ` Chao Gao 2022-04-12 13:21 ` Chao Gao 2022-04-12 13:21 ` Chao Gao 2022-04-12 13:33 ` Robin Murphy 2022-04-12 13:33 ` Robin Murphy 2022-04-13 1:02 ` Chao Gao 2022-04-13 1:02 ` Chao Gao 2022-04-13 4:59 ` Christoph Hellwig 2022-04-13 4:59 ` Christoph Hellwig 2022-04-13 5:46 ` Chao Gao 2022-04-13 5:46 ` Chao Gao 2022-04-13 5:49 ` Christoph Hellwig 2022-04-13 5:49 ` Christoph Hellwig 2022-04-13 13:10 ` Robin Murphy [this message] 2022-04-13 13:10 ` Robin Murphy 2022-04-13 16:44 ` Christoph Hellwig 2022-04-13 16:44 ` Christoph Hellwig
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