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Date:   Tue, 4 Jul 2023 18:50:51 +0800
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Subject: Re: [PATCH 8/8] videobuf2: handle non-contiguous DMA allocations
Content-Language: en-GB
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Christoph Hellwig <hch@lst.de>, Tomasz Figa <tfiga@chromium.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210302004624.31294-1-senozhatsky@chromium.org>
 <20210302004624.31294-9-senozhatsky@chromium.org>
From:   Hsia-Jun Li <Randy.Li@synaptics.com>
In-Reply-To: <20210302004624.31294-9-senozhatsky@chromium.org>
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Hello Sergey

I known this patch have been merged for a long time. I am thinking 
whether we need this flag in the new v4l2_ext_buffer.

On 3/2/21 08:46, Sergey Senozhatsky wrote:
> This adds support for new noncontiguous DMA API, which
> requires allocators to have two execution branches: one
> for the current API, and one for the new one.

There is no way we could allocate a coherent buffer in the platform 
except the x86.

Should we make this flag a platform compiling time fixed value?

And I didn't see Gstreamer nor FFmpeg uses it, it is obvious that they 
are running in many(almost all) embedded devices which are ARM.

>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> [hch: untested conversion to the ne API]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   .../common/videobuf2/videobuf2-dma-contig.c   | 141 +++++++++++++++---
>   1 file changed, 117 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> index 1e218bc440c6..d6a9f7b682f3 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> @@ -17,6 +17,7 @@
>   #include <linux/sched.h>
>   #include <linux/slab.h>
>   #include <linux/dma-mapping.h>
> +#include <linux/highmem.h>
>   
>   #include <media/videobuf2-v4l2.h>
>   #include <media/videobuf2-dma-contig.h>
> @@ -42,8 +43,14 @@ struct vb2_dc_buf {
>   	struct dma_buf_attachment	*db_attach;
>   
>   	struct vb2_buffer		*vb;
> +	unsigned int			non_coherent_mem:1;
>   };
>   
> +static bool vb2_dc_is_coherent(struct vb2_dc_buf *buf)
> +{
> +	return !buf->non_coherent_mem;
> +}
> +
>   /*********************************************/
>   /*        scatterlist table functions        */
>   /*********************************************/
> @@ -78,12 +85,21 @@ static void *vb2_dc_cookie(struct vb2_buffer *vb, void *buf_priv)
>   static void *vb2_dc_vaddr(struct vb2_buffer *vb, void *buf_priv)
>   {
>   	struct vb2_dc_buf *buf = buf_priv;
> -	struct dma_buf_map map;
> -	int ret;
>   
> -	if (!buf->vaddr && buf->db_attach) {
> -		ret = dma_buf_vmap(buf->db_attach->dmabuf, &map);
> -		buf->vaddr = ret ? NULL : map.vaddr;
> +	if (buf->vaddr)
> +		return buf->vaddr;
> +
> +	if (buf->db_attach) {
> +		struct dma_buf_map map;
> +
> +		if (!dma_buf_vmap(buf->db_attach->dmabuf, &map))
> +			buf->vaddr = map.vaddr;
> +	}
> +
> +	if (!vb2_dc_is_coherent(buf)) {
> +		buf->vaddr = dma_vmap_noncontiguous(buf->dev,
> +						    buf->size,
> +						    buf->dma_sgt);
>   	}
>   
>   	return buf->vaddr;
> @@ -101,13 +117,26 @@ static void vb2_dc_prepare(void *buf_priv)
>   	struct vb2_dc_buf *buf = buf_priv;
>   	struct sg_table *sgt = buf->dma_sgt;
>   
> +	/* This takes care of DMABUF and user-enforced cache sync hint */
>   	if (buf->vb->skip_cache_sync_on_prepare)
>   		return;
>   
> +	/*
> +	 * Coherent MMAP buffers do not need to be synced, unlike coherent
> +	 * USERPTR and non-coherent MMAP buffers.
> +	 */
> +	if (buf->vb->memory == V4L2_MEMORY_MMAP && vb2_dc_is_coherent(buf))
> +		return;
> +
>   	if (!sgt)
>   		return;
>   
> +	/* For both USERPTR and non-coherent MMAP */
>   	dma_sync_sgtable_for_device(buf->dev, sgt, buf->dma_dir);
> +
> +	/* Non-coherrent MMAP only */
> +	if (!vb2_dc_is_coherent(buf) && buf->vaddr)
> +		flush_kernel_vmap_range(buf->vaddr, buf->size);
>   }
>   
>   static void vb2_dc_finish(void *buf_priv)
> @@ -115,19 +144,46 @@ static void vb2_dc_finish(void *buf_priv)
>   	struct vb2_dc_buf *buf = buf_priv;
>   	struct sg_table *sgt = buf->dma_sgt;
>   
> +	/* This takes care of DMABUF and user-enforced cache sync hint */
>   	if (buf->vb->skip_cache_sync_on_finish)
>   		return;
>   
> +	/*
> +	 * Coherent MMAP buffers do not need to be synced, unlike coherent
> +	 * USERPTR and non-coherent MMAP buffers.
> +	 */
> +	if (buf->vb->memory == V4L2_MEMORY_MMAP && vb2_dc_is_coherent(buf))
> +		return;
> +
>   	if (!sgt)
>   		return;
>   
> +	/* For both USERPTR and non-coherent MMAP */
>   	dma_sync_sgtable_for_cpu(buf->dev, sgt, buf->dma_dir);
> +
> +	/* Non-coherrent MMAP only */
> +	if (!vb2_dc_is_coherent(buf) && buf->vaddr)
> +		invalidate_kernel_vmap_range(buf->vaddr, buf->size);
>   }
>   
>   /*********************************************/
>   /*        callbacks for MMAP buffers         */
>   /*********************************************/
>   
> +static void __vb2_dc_put(struct vb2_dc_buf *buf)
> +{
> +	if (vb2_dc_is_coherent(buf)) {
> +		dma_free_attrs(buf->dev, buf->size, buf->cookie,
> +			       buf->dma_addr, buf->attrs);
> +		return;
> +	}
> +
> +	if (buf->vaddr)
> +		dma_vunmap_noncontiguous(buf->dev, buf->vaddr);
> +	dma_free_noncontiguous(buf->dev, buf->size,
> +			       buf->dma_sgt, buf->dma_addr);
> +}
> +
>   static void vb2_dc_put(void *buf_priv)
>   {
>   	struct vb2_dc_buf *buf = buf_priv;
> @@ -139,17 +195,47 @@ static void vb2_dc_put(void *buf_priv)
>   		sg_free_table(buf->sgt_base);
>   		kfree(buf->sgt_base);
>   	}
> -	dma_free_attrs(buf->dev, buf->size, buf->cookie, buf->dma_addr,
> -		       buf->attrs);
> +	__vb2_dc_put(buf);
>   	put_device(buf->dev);
>   	kfree(buf);
>   }
>   
> +static int vb2_dc_alloc_coherent(struct vb2_dc_buf *buf)
> +{
> +	struct vb2_queue *q = buf->vb->vb2_queue;
> +
> +	buf->cookie = dma_alloc_attrs(buf->dev,
> +				      buf->size,
> +				      &buf->dma_addr,
> +				      GFP_KERNEL | q->gfp_flags,
> +				      buf->attrs);
> +	if (!buf->cookie)
> +		return -ENOMEM;
> +	if ((q->dma_attrs & DMA_ATTR_NO_KERNEL_MAPPING) == 0)
> +		buf->vaddr = buf->cookie;
> +	return 0;
> +}
> +
> +static int vb2_dc_alloc_non_coherent(struct vb2_dc_buf *buf)
> +{
> +	struct vb2_queue *q = buf->vb->vb2_queue;
> +
> +	buf->dma_sgt = dma_alloc_noncontiguous(buf->dev,
> +					       buf->size,
> +					       buf->dma_dir,
> +					       GFP_KERNEL | q->gfp_flags,
> +					       buf->attrs);
> +	if (!buf->dma_sgt)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
>   static void *vb2_dc_alloc(struct vb2_buffer *vb,
>   			  struct device *dev,
>   			  unsigned long size)
>   {
>   	struct vb2_dc_buf *buf;
> +	int ret;
>   
>   	if (WARN_ON(!dev))
>   		return ERR_PTR(-EINVAL);
> @@ -159,27 +245,28 @@ static void *vb2_dc_alloc(struct vb2_buffer *vb,
>   		return ERR_PTR(-ENOMEM);
>   
>   	buf->attrs = vb->vb2_queue->dma_attrs;
> -	buf->cookie = dma_alloc_attrs(dev, size, &buf->dma_addr,
> -				      GFP_KERNEL | vb->vb2_queue->gfp_flags,
> -				      buf->attrs);
> -	if (!buf->cookie) {
> -		dev_err(dev, "dma_alloc_coherent of size %ld failed\n", size);
> -		kfree(buf);
> -		return ERR_PTR(-ENOMEM);
> -	}
> -
> -	if ((buf->attrs & DMA_ATTR_NO_KERNEL_MAPPING) == 0)
> -		buf->vaddr = buf->cookie;
> +	buf->dma_dir = vb->vb2_queue->dma_dir;
> +	buf->vb = vb;
> +	buf->non_coherent_mem = vb->vb2_queue->non_coherent_mem;
>   
> +	buf->size = size;
>   	/* Prevent the device from being released while the buffer is used */
>   	buf->dev = get_device(dev);
> -	buf->size = size;
> -	buf->dma_dir = vb->vb2_queue->dma_dir;
> +
> +	if (vb2_dc_is_coherent(buf))
> +		ret = vb2_dc_alloc_coherent(buf);
> +	else
> +		ret = vb2_dc_alloc_non_coherent(buf);
> +
> +	if (ret) {
> +		dev_err(dev, "dma alloc of size %ld failed\n", size);
> +		kfree(buf);
> +		return ERR_PTR(-ENOMEM);
> +	}
>   
>   	buf->handler.refcount = &buf->refcount;
>   	buf->handler.put = vb2_dc_put;
>   	buf->handler.arg = buf;
> -	buf->vb = vb;
>   
>   	refcount_set(&buf->refcount, 1);
>   
> @@ -196,9 +283,12 @@ static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma)
>   		return -EINVAL;
>   	}
>   
> -	ret = dma_mmap_attrs(buf->dev, vma, buf->cookie,
> -		buf->dma_addr, buf->size, buf->attrs);
> -
> +	if (vb2_dc_is_coherent(buf))
> +		ret = dma_mmap_attrs(buf->dev, vma, buf->cookie, buf->dma_addr,
> +				     buf->size, buf->attrs);
> +	else
> +		ret = dma_mmap_noncontiguous(buf->dev, vma, buf->size,
> +					     buf->dma_sgt);
>   	if (ret) {
>   		pr_err("Remapping memory failed, error: %d\n", ret);
>   		return ret;
> @@ -390,6 +480,9 @@ static struct sg_table *vb2_dc_get_base_sgt(struct vb2_dc_buf *buf)
>   	int ret;
>   	struct sg_table *sgt;
>   
> +	if (!vb2_dc_is_coherent(buf))
> +		return buf->dma_sgt;
> +
>   	sgt = kmalloc(sizeof(*sgt), GFP_KERNEL);
>   	if (!sgt) {
>   		dev_err(buf->dev, "failed to alloc sg table\n");

-- 
Hsia-Jun(Randy) Li