Hello, On Wednesday, October 12, 2011 3:35 AM Krishna Reddy wrote: > >>It looks that You have simplified arm_iommu_map_sg() function too much. > >>The main advantage of the iommu is to map scattered memory pages into > >>contiguous dma address space. DMA-mapping is allowed to merge consecutive > >>entries in the scatter list if hardware supports that. > >>http://article.gmane.org/gmane.linux.kernel/1128416 > >I would update arm_iommu_map_sg() back to coalesce the sg list. > >>MMC drivers seem to be aware of coalescing the SG entries together as they are using > dma_sg_len(). > > I have updated the arm_iommu_map_sg() back to coalesce and fixed the issues with it. During > testing, I found out that mmc host driver doesn't support buffers bigger than 64K. To get the > device working, I had to break the sg entries coalesce when dma_length is about to go beyond > 64KB. Looks like Mmc host driver(sdhci.c) need to be fixed to handle buffers bigger than 64KB. > Should the clients be forced to handle bigger buffers or is there any better way to handle > these kind of issues? There is struct device_dma_parameters *dma_parms member of struct device. You can specify maximum segment size for the dma_map_sg function. This will of course complicate this function even more... Best regards -- Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>