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

[Robin Murphy]

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 at 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?

>> +		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