Re: [PATCH] videobuf-dma-contig: zero copy USERPTR support V3

[Mauro Carvalho Chehab <mchehab@infradead.org>]

Em Fri, 08 May 2009 17:53:10 +0900
Magnus Damm <magnus.damm@gmail.com> escreveu:

> From: Magnus Damm <damm@igel.co.jp>
> 
> This is V3 of the V4L2 videobuf-dma-contig USERPTR zero copy patch.
> 
> Since videobuf-dma-contig is designed to handle physically contiguous
> memory, this patch modifies the videobuf-dma-contig code to only accept
> a user space pointer to physically contiguous memory. For now only
> VM_PFNMAP vmas are supported, so forget hotplug.
> 
> On SuperH Mobile we use this with our sh_mobile_ceu_camera driver
> together with various multimedia accelerator blocks that are exported to
> user space using UIO. The UIO kernel code exports physically contiguous
> 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 and decoding.
> 
> Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>

> ---
> 
>  Needs the following patches (Thanks to Johannes Weiner and akpm):
>  - mm-introduce-follow_pte.patch
>  - mm-use-generic-follow_pte-in-follow_phys.patch
>  - mm-introduce-follow_pfn.patch
>  
>  Tested on SH7722 Migo-R with a hacked up capture.c
> 
>  Changes since V2:
>  - use follow_pfn(), drop mm/memory.c changes
> 
>  Changes since V1:
>  - minor cleanups and formatting changes
>  - use follow_phys() in videobuf-dma-contig instead of duplicating code
>  - since videobuf-dma-contig can be a module: EXPORT_SYMBOL(follow_phys)
>  - move CONFIG_HAVE_IOREMAP_PROT to always build follow_phys()
> 
>  drivers/media/video/videobuf-dma-contig.c |   78 +++++++++++++++++++++++++++--
>  1 file changed, 73 insertions(+), 5 deletions(-)
> 
> --- 0013/drivers/media/video/videobuf-dma-contig.c
> +++ work/drivers/media/video/videobuf-dma-contig.c	2009-05-08 15:57:21.000000000 +0900
> @@ -17,6 +17,7 @@
>  #include <linux/init.h>
>  #include <linux/module.h>
>  #include <linux/mm.h>
> +#include <linux/pagemap.h>
>  #include <linux/dma-mapping.h>
>  #include <media/videobuf-dma-contig.h>
>  
> @@ -25,6 +26,7 @@ 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 +110,66 @@ 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;
> +}
> +
> +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 = follow_pfn(vma, user_address, &this_pfn);
> +		if (ret)
> +			break;
> +
> +		if (pages_done == 0)
> +			mem->dma_handle = this_pfn << PAGE_SHIFT;
> +		else if (this_pfn != (prev_pfn + 1))
> +			ret = -EFAULT;
> +
> +		if (ret)
> +			break;
> +
> +		prev_pfn = this_pfn;
> +		user_address += PAGE_SIZE;
> +		pages_done++;
> +	}
> +
> +	if (!ret)
> +		mem->is_userptr = 1;
> +
> + out_up:
> +	up_read(&current->mm->mmap_sem);
> +
> +	return ret;
> +}
> +
>  static void *__videobuf_alloc(size_t size)
>  {
>  	struct videobuf_dma_contig_memory *mem;
> @@ -154,12 +216,11 @@ static int __videobuf_iolock(struct vide
>  	case V4L2_MEMORY_USERPTR:
>  		dev_dbg(q->dev, "%s memory method USERPTR\n", __func__);
>  
> -		/* The only USERPTR currently supported is the one needed for
> -		   read() method.
> -		 */
> +		/* handle pointer from user space */
>  		if (vb->baddr)
> -			return -EINVAL;
> +			return videobuf_dma_contig_user_get(mem, vb);
>  
> +		/* allocate memory for the read() method */
>  		mem->size = PAGE_ALIGN(vb->size);
>  		mem->vaddr = dma_alloc_coherent(q->dev, mem->size,
>  						&mem->dma_handle, GFP_KERNEL);
> @@ -386,7 +447,7 @@ void videobuf_dma_contig_free(struct vid
>  	   So, it should free memory only if the memory were allocated for
>  	   read() operation.
>  	 */
> -	if ((buf->memory != V4L2_MEMORY_USERPTR) || buf->baddr)
> +	if (buf->memory != V4L2_MEMORY_USERPTR)
>  		return;
>  
>  	if (!mem)
> @@ -394,6 +455,13 @@ void videobuf_dma_contig_free(struct vid
>  
>  	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);
>  
> +	/* handle user space pointer case */
> +	if (buf->baddr) {
> +		videobuf_dma_contig_user_put(mem);
> +		return;
> +	}
> +
> +	/* read() method */
>  	dma_free_coherent(q->dev, mem->size, mem->vaddr, mem->dma_handle);
>  	mem->vaddr = NULL;
>  }
> --
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Cheers,
Mauro

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