From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu_ops for GART/SMMU driver Date: Thu, 5 Jan 2012 14:46:31 +0000 Message-ID: <20120105144631.GV11810@n2100.arm.linux.org.uk> References: <1325747509-29665-1-git-send-email-hdoyu@nvidia.com> <20120105091718.3fb378b2a1d390f9dd63c396@nvidia.com> <20120105125326.GT11810@n2100.arm.linux.org.uk> <20120105.162930.604365154868332443.hdoyu@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20120105.162930.604365154868332443.hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Hiroshi Doyu Cc: "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linaro-mm-sig-bounces-cunTk1MwBs8s++Sfvej+rw@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: linux-tegra@vger.kernel.org On Thu, Jan 05, 2012 at 03:29:30PM +0100, Hiroshi Doyu wrote: > Ok, the above function order should be as below? > > page = alloc_page(GFP_KERNEL); > cpu_addr = kmap(page); > memset(cpu_addr, 0xa5, PAGE_SIZE); > dma_addr = dma_map_page(dev, page, 0, PAGE_SIZE, DMA_TO_DEVICE); > < expect GPU does something > > dma_unmap_page(dev, dma_addr, PAGE_SIZE, DMA_TO_DEVICE); > < CPU can access data here again> > kunmap(cpu_addr); > __free_page(page); That should work, but it's not particularly nice to wrap kmap around the DMA API. Bear in mind that alloc_page(GFP_KERNEL) will always give you a lowmem page. So, you might as well do: page = alloc_page(GFP_KERNEL); cpu_addr = page_address(page); memset() dma_addr = dma_map_single(dev, cpu_addr, PAGE_SIZE, DMA_TO_DEVICE); < GPU access > dma_unmap_single(dev, dma_ddr, PAGE_SIZE, DMA_TO_DEVICE); < CPU access > __free_page(page); and this doesn't raise any issues with kmap vs DMA API.