Messages in this thread | | | Date | Wed, 10 Feb 2010 15:28:17 -0800 | From | Abhijeet Dharmapurikar <> | Subject | Re: [RFC 0/2] fix dma_map_sg not to do barriers for each buffer |
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Russell King - ARM Linux wrote: > On Wed, Feb 10, 2010 at 12:37:28PM -0800, adharmap@codeaurora.org wrote: >> From: Abhijeet Dharmapurikar <adharmap@quicinc.com> >> >> Please refer to the post here >> http://lkml.org/lkml/2010/1/4/347 >> >> These changes are to introduce barrierless dma_map_area and dma_unmap_area and >> use them to map the buffers in the scatterlist. For the last buffer, call >> the normal dma_map_area(aka with barriers) effectively executing the barrier >> at the end of the operation. > > What if we make dma_map_area and dma_unmap_area both be barrier-less, > and instead have a separate dma_barrier method - eg, something like the > attached? > > This might allow for better I-cache usage by not having to duplicate the > DMA cache coherence functions.
Agree, thanks for pointing this and for the patch.
> > @@ -369,6 +372,7 @@ static inline dma_addr_t dma_map_page(struct device *dev, struct page *page, > BUG_ON(!valid_dma_direction(dir)); > > __dma_page_cpu_to_dev(page, offset, size, dir); > + __dma_barrier(dir); > > return page_to_dma(dev, page) + offset; > }
dma_map_page is going to execute the barrier here.
> /** > * dma_map_sg - map a set of SG buffers for streaming mode DMA > * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices > @@ -537,6 +544,9 @@ int dma_map_sg(struct device *dev, struct scatterlist *sg, int nents, > if (dma_mapping_error(dev, s->dma_address)) > goto bad_mapping; > } > + > + __dma_barrier(dir); > + > return nents;
This would call the barrier in addition to the ones executed by dma_map_page.
We would need to call __dma_page_cpu_to_dev instead of dma_map_page and do the barrier before returning.
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