On Mon, Apr 20, 2009 at 07:00:03PM +0900, Magnus Damm wrote:
> From: Magnus Damm <[email protected]>
>
> Zero copy video frame capture from user space using V4L2 USERPTR.
>
> This patch adds USERPTR support to the videobuf-dma-contig buffer code.
> Since videobuf-dma-contig is designed to handle physically contiguous
> memory, this patch modifies the videobuf-dma-contig code to only accept
> a pointer physically contiguous memory. For now only VM_PFNMAP vmas are
> supported, so forget hotplug.
>
> On SuperH Mobile we use this approach for our V4L2 CEU driver together
> with various multimedia accelerator blocks that are exported to user
> space using UIO. The UIO kernel code exports physically contiugous memory
> to user space and lets the user space application mmap() this memory and
> pass a pointer using the USERPTR interface for V4L2 zero copy operation.
>
> With this approach we support zero copy capture, hardware scaling and
> various forms of hardware encoding.
>
> Hopefully this patch is useful for other SoCs. For user space example
> code I suggest having a look at the USERPTR implementation in capture.c.
>
> Any comments? Does anyone need to use memory backed by struct page?
>
> Signed-off-by: Magnus Damm <[email protected]>
> ---
>
> drivers/media/video/videobuf-dma-contig.c | 138
> +++++++++++++++++++++++++++--
> 1 file changed, 131 insertions(+), 7 deletions(-)
>
> --- 0001/drivers/media/video/videobuf-dma-contig.c
> +++ work/drivers/media/video/videobuf-dma-contig.c 2009-04-20
> 18:04:32.000000000 +0900
> @@ -17,6 +17,8 @@
> #include <linux/init.h>
> #include <linux/module.h>
> #include <linux/mm.h>
> +#include <linux/hugetlb.h>
> +#include <linux/pagemap.h>
> #include <linux/dma-mapping.h>
> #include <media/videobuf-dma-contig.h>
>
> @@ -25,6 +27,7 @@ struct videobuf_dma_contig_memory {
> void *vaddr;
> dma_addr_t dma_handle;
> unsigned long size;
> + int is_userptr;
> };
>
> #define MAGIC_DC_MEM 0x0733ac61
> @@ -108,6 +111,117 @@ static struct vm_operations_struct video
> .close = videobuf_vm_close,
> };
>
> +static void videobuf_dma_contig_user_put(struct videobuf_dma_contig_memory
> *mem)
> +{
> + mem->is_userptr = 0;
> + mem->dma_handle = 0;
> + mem->size = 0;
> +}
> +
> +/* modelled after follow_phys() in mm/memory.c */
> +static int get_pfn(struct vm_area_struct *vma,
> + unsigned long address, unsigned long *pfnp)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + pgd_t *pgd;
> + pud_t *pud;
> + pmd_t *pmd;
> + pte_t *ptep, pte;
> + spinlock_t *ptl;
> +
> + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
> + goto no_page_table;
> +
> + pgd = pgd_offset(mm, address);
> + if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
> + goto no_page_table;
> +
> + pud = pud_offset(pgd, address);
> + if (pud_none(*pud) || unlikely(pud_bad(*pud)))
> + goto no_page_table;
> +
> + pmd = pmd_offset(pud, address);
> + if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
> + goto no_page_table;
> +
> + /* We cannot handle huge page PFN maps. Luckily they don't exist. */
> + if (pmd_huge(*pmd))
> + goto no_page_table;
> +
> + ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> + if (!ptep)
> + goto no_page_table;
> +
> + pte = *ptep;
> + if (!pte_present(pte))
> + goto unlock;
> +
> + *pfnp = pte_pfn(pte);
> + pte_unmap_unlock(ptep, ptl);
> + return 0;
> +unlock:
> + pte_unmap_unlock(ptep, ptl);
> +no_page_table:
> + return -EINVAL;
> +}
It would be nice to have a follow_pfn() instead that shares its body
with follow_phys().
> +static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory
> *mem,
> + struct videobuf_buffer *vb)
> +{
> + struct mm_struct *mm = current->mm;
> + struct vm_area_struct *vma;
> + unsigned long prev_pfn, this_pfn;
> + unsigned long pages_done, user_address;
> + int ret;
> +
> + mem->size = PAGE_ALIGN(vb->size);
> + mem->is_userptr = 0;
> + ret = -EINVAL;
> +
> + down_read(&mm->mmap_sem);
> +
> + vma = find_vma(mm, vb->baddr);
> + if (!vma)
> + goto out_up;
> +
> + if ((vb->baddr + mem->size) > vma->vm_end)
> + goto out_up;
> +
> + pages_done = 0;
> + prev_pfn = 0; /* kill warning */
> + user_address = vb->baddr;
> +
> + while (pages_done < (mem->size >> PAGE_SHIFT)) {
> + ret = get_pfn(vma, user_address, &this_pfn);
> + if (ret)
> + break;
> +
> + if (pages_done == 0) {
> + prev_pfn = this_pfn;
> + mem->dma_handle = this_pfn << PAGE_SHIFT;
> + } else {
> + if (this_pfn != (prev_pfn + 1))
> + ret = -EFAULT;
} else if (...) ?
> + }
> +
> + if (ret)
> + break;
> +
> + prev_pfn = this_pfn;
> + user_address += PAGE_SIZE;
> + pages_done++;
> + }
> +
> + if (!ret && pages_done)
If ret is zero, pages_done is always non-zero.
> + mem->is_userptr = 1;
> +
> + out_up:
> + up_read(¤t->mm->mmap_sem);
> +
> + return ret;
> +}
> +
Hannes
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