Re: [RFC RESEND 10/11] vb2: dma-contig: Let drivers decide DMA attrs of MMAP and USERPTR bufs

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

Thank you for the patch.

On Friday 11 Sep 2015 14:50:33 Sakari Ailus wrote:
> The desirable DMA attributes are not generic for all devices using
> Videobuf2 contiguous DMA ops. Let the drivers decide.
> 
> This change also results in MMAP buffers always having an sg_table
> (dma_sgt field).
> 
> Also arrange the header files alphabetically.
> 
> As a result, also the DMA-BUF exporter must provide ops for synchronising
> the cache. This adds begin_cpu_access and end_cpu_access ops to
> vb2_dc_dmabuf_ops.
> 
> The driver API changes were done using the following coccinelle spatch:
> 
> @@
> expression E;
> @@
> 
> - vb2_dma_contig_init_ctx(E)
> + vb2_dma_contig_init_ctx(E, NULL)

I wanted to mention that this patch includes no driver change, but the 
vb2_dma_contig_init_ctx() has disappeared now, replaced by an attrs attribute 
to the .alloc() operation. This, and the fact that the kernel has moved from 
struct dma_attrs to unsigned long to store the DMA attributes, generates a lot 
of conflicts. I'll review the rebased version.

> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/v4l2-core/videobuf2-dma-contig.c | 104 +++++++++++++++-------
>  include/media/videobuf2-dma-contig.h           |   3 +-
>  2 files changed, 79 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> b/drivers/media/v4l2-core/videobuf2-dma-contig.c index 65bc687..65ee122
> 100644
> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> @@ -11,11 +11,11 @@
>   */
> 
>  #include <linux/dma-buf.h>
> +#include <linux/dma-mapping.h>
>  #include <linux/module.h>
>  #include <linux/scatterlist.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> -#include <linux/dma-mapping.h>
> 
>  #include <media/videobuf2-core.h>
>  #include <media/videobuf2-dma-contig.h>
> @@ -23,6 +23,7 @@
> 
>  struct vb2_dc_conf {
>  	struct device		*dev;
> +	struct dma_attrs	attrs;
>  };
> 
>  struct vb2_dc_buf {
> @@ -34,6 +35,7 @@ struct vb2_dc_buf {
>  	struct sg_table			*dma_sgt;
> 
>  	/* MMAP related */
> +	struct dma_attrs		*attrs;
>  	struct vb2_vmarea_handler	handler;
>  	atomic_t			refcount;
> 
> @@ -135,8 +137,12 @@ static void vb2_dc_prepare(void *buf_priv)
>  	struct vb2_dc_buf *buf = buf_priv;
>  	struct sg_table *sgt = buf->dma_sgt;
> 
> -	/* DMABUF exporter will flush the cache for us */
> -	if (!buf->vma)
> +	/*
> +	 * DMABUF exporter will flush the cache for us; only USERPTR
> +	 * and MMAP buffers with non-coherent memory will be flushed.
> +	 */
> +	if (!buf->attrs ||
> +	    !dma_get_attr(DMA_ATTR_NON_CONSISTENT, buf->attrs))
>  		return;
> 
>  	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> @@ -147,8 +153,12 @@ static void vb2_dc_finish(void *buf_priv)
>  	struct vb2_dc_buf *buf = buf_priv;
>  	struct sg_table *sgt = buf->dma_sgt;
> 
> -	/* DMABUF exporter will flush the cache for us */
> -	if (!buf->vma)
> +	/*
> +	 * DMABUF exporter will flush the cache for us; only USERPTR
> +	 * and MMAP buffers with non-coherent memory will be flushed.
> +	 */
> +	if (!buf->attrs ||
> +	    !dma_get_attr(DMA_ATTR_NON_CONSISTENT, buf->attrs))
>  		return;
> 
>  	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> @@ -169,7 +179,8 @@ static void vb2_dc_put(void *buf_priv)
>  		sg_free_table(buf->dma_sgt);
>  		kfree(buf->dma_sgt);
>  	}
> -	dma_free_coherent(buf->dev, buf->size, buf->vaddr, buf->dma_addr);
> +	dma_free_attrs(buf->dev, buf->size, buf->vaddr, buf->dma_addr,
> +		       buf->attrs);
>  	put_device(buf->dev);
>  	kfree(buf);
>  }
> @@ -185,14 +196,25 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned
> long size, if (!buf)
>  		return ERR_PTR(-ENOMEM);
> 
> -	buf->vaddr = dma_alloc_coherent(dev, size, &buf->dma_addr,
> -						GFP_KERNEL | gfp_flags);
> +	buf->attrs = &conf->attrs;
> +
> +	buf->vaddr = dma_alloc_attrs(dev, size, &buf->dma_addr,
> +				     GFP_KERNEL | gfp_flags, buf->attrs);
>  	if (!buf->vaddr) {
> -		dev_err(dev, "dma_alloc_coherent of size %ld failed\n", size);
> +		dev_err(dev, "dma_alloc_attrs of size %ld failed\n", size);
>  		kfree(buf);
>  		return ERR_PTR(-ENOMEM);
>  	}
> 
> +	if (dma_get_attr(DMA_ATTR_NON_CONSISTENT, buf->attrs)) {
> +		buf->dma_sgt = vb2_dc_get_base_sgt(buf);
> +		if (!buf->dma_sgt) {
> +			dma_free_attrs(dev, size, buf->vaddr, buf->dma_addr,
> +				       buf->attrs);
> +			return ERR_PTR(-ENOMEM);
> +		}
> +	}
> +
>  	/* Prevent the device from being released while the buffer is used */
>  	buf->dev = get_device(dev);
>  	buf->size = size;
> @@ -223,8 +245,8 @@ static int vb2_dc_mmap(void *buf_priv, struct
> vm_area_struct *vma) */
>  	vma->vm_pgoff = 0;
> 
> -	ret = dma_mmap_coherent(buf->dev, vma, buf->vaddr,
> -		buf->dma_addr, buf->size);
> +	ret = dma_mmap_attrs(buf->dev, vma, buf->vaddr, buf->dma_addr,
> +			     buf->size, buf->attrs);
> 
>  	if (ret) {
>  		pr_err("Remapping memory failed, error: %d\n", ret);
> @@ -370,6 +392,34 @@ static void *vb2_dc_dmabuf_ops_kmap(struct dma_buf
> *dbuf, unsigned long pgnum) return buf->vaddr + pgnum * PAGE_SIZE;
>  }
> 
> +static int vb2_dc_dmabuf_ops_begin_cpu_access(
> +	struct dma_buf *dbuf, size_t start, size_t len,
> +	enum dma_data_direction direction)
> +{
> +	struct vb2_dc_buf *buf = dbuf->priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	if (!dma_get_attr(DMA_ATTR_NON_CONSISTENT, buf->attrs))
> +		return 0;
> +
> +	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +
> +	return 0;
> +}
> +
> +static void vb2_dc_dmabuf_ops_end_cpu_access(
> +	struct dma_buf *dbuf, size_t start, size_t len,
> +	enum dma_data_direction direction)
> +{
> +	struct vb2_dc_buf *buf = dbuf->priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	if (!dma_get_attr(DMA_ATTR_NON_CONSISTENT, buf->attrs))
> +		return;
> +
> +	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +}
> +
>  static void *vb2_dc_dmabuf_ops_vmap(struct dma_buf *dbuf)
>  {
>  	struct vb2_dc_buf *buf = dbuf->priv;
> @@ -390,6 +440,8 @@ static struct dma_buf_ops vb2_dc_dmabuf_ops = {
>  	.unmap_dma_buf = vb2_dc_dmabuf_ops_unmap,
>  	.kmap = vb2_dc_dmabuf_ops_kmap,
>  	.kmap_atomic = vb2_dc_dmabuf_ops_kmap,
> +	.begin_cpu_access = vb2_dc_dmabuf_ops_begin_cpu_access,
> +	.end_cpu_access = vb2_dc_dmabuf_ops_end_cpu_access,
>  	.vmap = vb2_dc_dmabuf_ops_vmap,
>  	.mmap = vb2_dc_dmabuf_ops_mmap,
>  	.release = vb2_dc_dmabuf_ops_release,
> @@ -514,15 +566,13 @@ static void vb2_dc_put_userptr(void *buf_priv)
>  	struct sg_table *sgt = buf->dma_sgt;
> 
>  	if (sgt) {
> -		DEFINE_DMA_ATTRS(attrs);
> -
> -		dma_set_attr(DMA_ATTR_SKIP_CPU_SYNC, &attrs);
>  		/*
> -		 * No need to sync to CPU, it's already synced to the CPU
> -		 * since the finish() memop will have been called before this.
> +		 * Don't ask to skip cache sync in case if the user
> +		 * did ask to skip cache flush the last time the
> +		 * buffer was dequeued.
>  		 */
>  		dma_unmap_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
> -				   buf->dma_dir, &attrs);
> +				   buf->dma_dir, buf->attrs);
>  		if (!vma_is_io(buf->vma))
>  			vb2_dc_sgt_foreach_page(sgt, vb2_dc_put_dirty_page);
> 
> @@ -579,9 +629,6 @@ static void *vb2_dc_get_userptr(void *alloc_ctx,
> unsigned long vaddr, struct sg_table *sgt;
>  	unsigned long contig_size;
>  	unsigned long dma_align = dma_get_cache_alignment();
> -	DEFINE_DMA_ATTRS(attrs);
> -
> -	dma_set_attr(DMA_ATTR_SKIP_CPU_SYNC, &attrs);
> 
>  	/* Only cache aligned DMA transfers are reliable */
>  	if (!IS_ALIGNED(vaddr | size, dma_align)) {
> @@ -598,6 +645,8 @@ static void *vb2_dc_get_userptr(void *alloc_ctx,
> unsigned long vaddr, if (!buf)
>  		return ERR_PTR(-ENOMEM);
> 
> +	buf->attrs = &conf->attrs;
> +
>  	buf->dev = conf->dev;
>  	buf->dma_dir = dma_dir;
> 
> @@ -667,12 +716,8 @@ static void *vb2_dc_get_userptr(void *alloc_ctx,
> unsigned long vaddr, kfree(pages);
>  	pages = NULL;
> 
> -	/*
> -	 * No need to sync to the device, this will happen later when the
> -	 * prepare() memop is called.
> -	 */
>  	sgt->nents = dma_map_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
> -				      buf->dma_dir, &attrs);
> +				      buf->dma_dir, buf->attrs);
>  	if (sgt->nents <= 0) {
>  		pr_err("failed to map scatterlist\n");
>  		ret = -EIO;
> @@ -695,7 +740,7 @@ static void *vb2_dc_get_userptr(void *alloc_ctx,
> unsigned long vaddr,
> 
>  fail_map_sg:
>  	dma_unmap_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
> -			   buf->dma_dir, &attrs);
> +			   buf->dma_dir, buf->attrs);
> 
>  fail_sgt_init:
>  	if (!vma_is_io(buf->vma))
> @@ -856,7 +901,7 @@ const struct vb2_mem_ops vb2_dma_contig_memops = {
>  };
>  EXPORT_SYMBOL_GPL(vb2_dma_contig_memops);
> 
> -void *vb2_dma_contig_init_ctx(struct device *dev)
> +void *vb2_dma_contig_init_ctx(struct device *dev, struct dma_attrs *attrs)
>  {
>  	struct vb2_dc_conf *conf;
> 
> @@ -866,6 +911,11 @@ void *vb2_dma_contig_init_ctx(struct device *dev)
> 
>  	conf->dev = dev;
> 
> +	if (!attrs)
> +		init_dma_attrs(&conf->attrs);
> +	else
> +		conf->attrs = *attrs;
> +
>  	return conf;
>  }
>  EXPORT_SYMBOL_GPL(vb2_dma_contig_init_ctx);
> diff --git a/include/media/videobuf2-dma-contig.h
> b/include/media/videobuf2-dma-contig.h index 8197f87..1b85282 100644
> --- a/include/media/videobuf2-dma-contig.h
> +++ b/include/media/videobuf2-dma-contig.h
> @@ -24,7 +24,8 @@ vb2_dma_contig_plane_dma_addr(struct vb2_buffer *vb,
> unsigned int plane_no) return *addr;
>  }
> 
> -void *vb2_dma_contig_init_ctx(struct device *dev);
> +void *vb2_dma_contig_init_ctx(struct device *dev,
> +			      struct dma_attrs *attrs);
>  void vb2_dma_contig_cleanup_ctx(void *alloc_ctx);
> 
>  extern const struct vb2_mem_ops vb2_dma_contig_memops;

-- 
Regards,

Laurent Pinchart