[PATCH v2 2/4] iommu: Implement common IOMMU ops for DMA mapping

[yong.wu@mediatek.com (Yong Wu)]

On Thu, 2015-06-18 at 17:54 +0100, Robin Murphy wrote:
> On 18/06/15 16:00, Yong Wu wrote:
> > Hi Robin,
> >      while our drm test, we meet a problem while dma-mmap.
> >
> >   On Thu, 2015-06-11 at 16:54 +0100, Robin Murphy wrote:
> >> Taking inspiration from the existing arch/arm code, break out some
> >> generic functions to interface the DMA-API to the IOMMU-API. This will
> >> do the bulk of the heavy lifting for IOMMU-backed dma-mapping.
> >>
> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> >> ---
> >>   drivers/iommu/Kconfig     |   7 +
> >>   drivers/iommu/Makefile    |   1 +
> >>   drivers/iommu/dma-iommu.c | 560 ++++++++++++++++++++++++++++++++++++++++++++++
> >>   include/linux/dma-iommu.h |  94 ++++++++
> >>   4 files changed, 662 insertions(+)
> >>   create mode 100644 drivers/iommu/dma-iommu.c
> >>   create mode 100644 include/linux/dma-iommu.h
> >>
> > [snip]
> >> +/**
> >> + * iommu_dma_mmap - Map a buffer into provided user VMA
> >> + * @pages: Array representing buffer from iommu_dma_alloc()
> >> + * @size: Size of buffer in bytes
> >> + * @vma: VMA describing requested userspace mapping
> >> + *
> >> + * Maps the pages of the buffer in @pages into @vma. The caller is responsible
> >> + * for verifying the correct size and protection of @vma beforehand.
> >> + */
> >> +
> >> +int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma)
> >> +{
> >> +	unsigned long uaddr = vma->vm_start;
> >> +	unsigned int i, count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> >> +	int ret = -ENXIO;
> >> +
> >> +	for (i = vma->vm_pgoff; i < count && uaddr < vma->vm_end; i++) {
> > Is it :  for (i = 0; i < count && uaddr < vma->vm_end; i++)
> 
> According to the patches at [1], respecting vma->pgoff is necessary for 
> users who only want to mmap part of the buffer. Does your DRM driver by 
> any chance need the same fix as the Rockchip one?
Thanks. We will try to add it.
> 
> >> +		ret = vm_insert_page(vma, uaddr, pages[i]);
> >> +		if (ret)
> >> +			break;
> >> +		uaddr += PAGE_SIZE;
> >> +	}
> >> +	return ret;
> >> +}
> >> +
> 
> And to save another email:
> 
>  >> +	if (WARN_ON(!area || area->pages))
>  > Is it:    if (WARN_ON(!area || !area->pages))
>  >> +		return -ENXIO;
> 
> You're absolutely right, thanks. I've got a couple more bugfixes in 
> progress too, so I'll try to get an updated branch pushed out soon; I'll 
> hold off posting a v3 to the list until after the upcoming merge window, 
> though.
> 
> Robin.
> 
> [1]:http://thread.gmane.org/gmane.linux.kernel/1932343
>