Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Cho KyongHo
On Tue, Aug 18, 2020 at 05:10:06PM +0100, Christoph Hellwig wrote: > On Tue, Aug 18, 2020 at 11:07:57AM +0100, Will Deacon wrote: > > > > so I'm not sure > > > > that we should be complicating the implementation like this to try to > > > > make it "fast". > > > > > > > I agree that this patch make

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Cho KyongHo
On Tue, Aug 18, 2020 at 11:07:57AM +0100, Will Deacon wrote: > On Tue, Aug 18, 2020 at 06:37:39PM +0900, Cho KyongHo wrote: > > On Tue, Aug 18, 2020 at 09:28:53AM +0100, Will Deacon wrote: > > > On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > > > > Cache maintenance operations in the

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Christoph Hellwig
On Tue, Aug 18, 2020 at 11:07:57AM +0100, Will Deacon wrote: > > > so I'm not sure > > > that we should be complicating the implementation like this to try to > > > make it "fast". > > > > > I agree that this patch makes the implementation of dma API a bit more > > but I don't think this does not

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Will Deacon
On Tue, Aug 18, 2020 at 06:37:39PM +0900, Cho KyongHo wrote: > On Tue, Aug 18, 2020 at 09:28:53AM +0100, Will Deacon wrote: > > On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > > > Cache maintenance operations in the most of CPU architectures needs > > > memory barrier after the cache

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Cho KyongHo
On Tue, Aug 18, 2020 at 09:37:20AM +0100, Christoph Hellwig wrote: > On Tue, Aug 18, 2020 at 09:28:53AM +0100, Will Deacon wrote: > > On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > > > Cache maintenance operations in the most of CPU architectures needs > > > memory barrier after the

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Cho KyongHo
On Tue, Aug 18, 2020 at 09:28:53AM +0100, Will Deacon wrote: > On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > > Cache maintenance operations in the most of CPU architectures needs > > memory barrier after the cache maintenance for the DMAs to view the > > region of the memory correc

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Christoph Hellwig
On Tue, Aug 18, 2020 at 09:28:53AM +0100, Will Deacon wrote: > On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > > Cache maintenance operations in the most of CPU architectures needs > > memory barrier after the cache maintenance for the DMAs to view the > > region of the memory correc

Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Will Deacon
On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > Cache maintenance operations in the most of CPU architectures needs > memory barrier after the cache maintenance for the DMAs to view the > region of the memory correctly. The problem is that memory barrier is > very expensive and dma_[

[PATCH 1/2] dma-mapping: introduce relaxed version of dma sync

2020-08-18 Thread Cho KyongHo
Cache maintenance operations in the most of CPU architectures needs memory barrier after the cache maintenance for the DMAs to view the region of the memory correctly. The problem is that memory barrier is very expensive and dma_[un]map_sg() and dma_sync_sg_for_{device|cpu}() involves the memory ba