On 4/16/2014 11:11 AM, Lin Ming wrote: > Hi Peter, > > I have a performance problem(on ARM board) that cpu is very bus at > cache invalidation. > So I'm trying to alloc an uncached memory to eliminate cache invalidation. > > But I also have problem with dma_alloc_coherent(). > If I don't use dma_alloc_coherent(), is it OK to use below code to > alloc uncached memory? > > struct page *page; > pgd_t *pgd; > pud_t *pud; > pmd_t *pmd; > pte_t *pte; > void *cpu_addr; > dma_addr_t dma_addr; > unsigned int vaddr; > > cpu_addr = kmalloc(PAGE_SIZE, GFP_KERNEL); > dma_addr = pci_map_single(NULL, cpu_addr, PAGE_SIZE, (int)DMA_FROM_DEVICE); > vaddr = (unsigned int)uncached->cpu_addr; > pgd = pgd_offset_k(vaddr); > pud = pud_offset(pgd, vaddr); > pmd = pmd_offset(pud, vaddr); > pte = pte_offset_kernel(pmd, vaddr); > page = virt_to_page(vaddr); > set_pte_ext(pte, mk_pte(page, pgprot_dmacoherent(pgprot_kernel)), 0); > > /* This kmalloc memory won't be freed */ > No, that will not work. lowmem pages are mapped with 1MB sections underneath which cannot be (easily) changed at runtime. You really want to be using dma_alloc_coherent here. Laura -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>