Re: [PATCH 8/8] videobuf2: handle non-contiguous DMA allocations

Hsia-Jun Li <Randy.Li@xxxxxxxxxxxxx> · Tue, 4 Jul 2023 18:50:51 +0800

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@xxxxxxxxxxxx>
[hch: untested conversion to the ne API]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
  .../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







