linux-kernel - Re: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu

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Message-ID: <20120111.162440.1854857348878391112.hdoyu@nvidia.com>
Date:	Wed, 11 Jan 2012 15:24:40 +0100
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"linux@....linux.org.uk" <linux@....linux.org.uk>
CC:	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linaro-mm-sig-bounces@...ts.linaro.org" 
	<linaro-mm-sig-bounces@...ts.linaro.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu_ops for GART/SMMU
 driver

From: Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu_ops for GART/SMMU driver
Date: Thu, 5 Jan 2012 15:46:31 +0100
Message-ID: <20120105144631.GV11810@...00.arm.linux.org.uk>

> 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.

Attached the update one just in case that someone wants to use it for theirs.

View attachment "0001-NOT-FOR-MERGE-TEST-Simple-dma-iommu-mapping-API-TEST.patch" of type "text/x-patch" (6451 bytes)