media: media/v4l2: remove V4L2_FLAG_MEMORY_NON_CONSISTENT flag

The patch partially reverts some of the UAPI bits of the buffer
cache management hints. Namely, the queue consistency (memory
coherency) user-space hint because, as it turned out, the kernel
implementation of this feature was misusing DMA_ATTR_NON_CONSISTENT.

The patch reverts both kernel and user space parts: removes the
DMA consistency attr functions, rolls back changes to v4l2_requestbuffers,
v4l2_create_buffers structures and corresponding UAPI functions
(plus compat32 layer) and cleans up the documentation.

[hverkuil: fixed a few typos in the commit log]
[hverkuil: fixed vb2_core_reqbufs call in drivers/media/dvb-core/dvb_vb2.c]
[mchehab: fixed a typo in the commit log: revers->reverts]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/v4l/buffer.rst

@@ -701,23 +701,6 @@ Memory Consistency Flags
     :stub-columns: 0
     :widths:       3 1 4
 
-    * .. _`V4L2-FLAG-MEMORY-NON-CONSISTENT`:
-
-      - ``V4L2_FLAG_MEMORY_NON_CONSISTENT``
-      - 0x00000001
-      - A buffer is allocated either in consistent (it will be automatically
-	coherent between the CPU and the bus) or non-consistent memory. The
-	latter can provide performance gains, for instance the CPU cache
-	sync/flush operations can be avoided if the buffer is accessed by the
-	corresponding device only and the CPU does not read/write to/from that
-	buffer. However, this requires extra care from the driver -- it must
-	guarantee memory consistency by issuing a cache flush/sync when
-	consistency is needed. If this flag is set V4L2 will attempt to
-	allocate the buffer in non-consistent memory. The flag takes effect
-	only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the
-	queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS
-	<V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability.
-
 .. c:type:: v4l2_memory
 
 enum v4l2_memory

Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst

@@ -120,13 +120,9 @@ than the number requested.
 	If you want to just query the capabilities without making any
 	other changes, then set ``count`` to 0, ``memory`` to
 	``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
-    * - __u32
-      - ``flags``
-      - Specifies additional buffer management attributes.
-	See :ref:`memory-flags`.
 
     * - __u32
-      - ``reserved``\ [6]
+      - ``reserved``\ [7]
       - A place holder for future extensions. Drivers and applications
 	must set the array to zero.
 

Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst

@@ -112,17 +112,10 @@ aborting or finishing any DMA in progress, an implicit
 	``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
 	free any previously allocated buffers, so this is typically something
 	that will be done at the start of the application.
-    * - union {
-      - (anonymous)
-    * - __u32
-      - ``flags``
-      - Specifies additional buffer management attributes.
-	See :ref:`memory-flags`.
     * - __u32
       - ``reserved``\ [1]
-      - Kept for backwards compatibility. Use ``flags`` instead.
-    * - }
-      -
+      - A place holder for future extensions. Drivers and applications
+	must set the array to zero.
 
 .. tabularcolumns:: |p{6.1cm}|p{2.2cm}|p{8.7cm}|
 
@@ -169,7 +162,6 @@ aborting or finishing any DMA in progress, an implicit
       - This capability is set by the driver to indicate that the queue supports
         cache and memory management hints. However, it's only valid when the
         queue is used for :ref:`memory mapping <mmap>` streaming I/O. See
-        :ref:`V4L2_FLAG_MEMORY_NON_CONSISTENT <V4L2-FLAG-MEMORY-NON-CONSISTENT>`,
         :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>` and
         :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>`.
 

drivers/media/common/videobuf2/videobuf2-core.c

@@ -721,39 +721,14 @@ int vb2_verify_memory_type(struct vb2_queue *q,
 }
 EXPORT_SYMBOL(vb2_verify_memory_type);
 
-static void set_queue_consistency(struct vb2_queue *q, bool consistent_mem)
-{
-	q->dma_attrs &= ~DMA_ATTR_NON_CONSISTENT;
-
-	if (!vb2_queue_allows_cache_hints(q))
-		return;
-	if (!consistent_mem)
-		q->dma_attrs |= DMA_ATTR_NON_CONSISTENT;
-}
-
-static bool verify_consistency_attr(struct vb2_queue *q, bool consistent_mem)
-{
-	bool queue_is_consistent = !(q->dma_attrs & DMA_ATTR_NON_CONSISTENT);
-
-	if (consistent_mem != queue_is_consistent) {
-		dprintk(q, 1, "memory consistency model mismatch\n");
-		return false;
-	}
-	return true;
-}
-
 int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
-		     unsigned int flags, unsigned int *count)
+		     unsigned int *count)
 {
 	unsigned int num_buffers, allocated_buffers, num_planes = 0;
 	unsigned plane_sizes[VB2_MAX_PLANES] = { };
-	bool consistent_mem = true;
 	unsigned int i;
 	int ret;
 
-	if (flags & V4L2_FLAG_MEMORY_NON_CONSISTENT)
-		consistent_mem = false;
-
 	if (q->streaming) {
 		dprintk(q, 1, "streaming active\n");
 		return -EBUSY;
@@ -765,8 +740,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
 	}
 
 	if (*count == 0 || q->num_buffers != 0 ||
-	    (q->memory != VB2_MEMORY_UNKNOWN && q->memory != memory) ||
-	    !verify_consistency_attr(q, consistent_mem)) {
+	    (q->memory != VB2_MEMORY_UNKNOWN && q->memory != memory)) {
 		/*
 		 * We already have buffers allocated, so first check if they
 		 * are not in use and can be freed.
@@ -803,7 +777,6 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
 	num_buffers = min_t(unsigned int, num_buffers, VB2_MAX_FRAME);
 	memset(q->alloc_devs, 0, sizeof(q->alloc_devs));
 	q->memory = memory;
-	set_queue_consistency(q, consistent_mem);
 
 	/*
 	 * Ask the driver how many buffers and planes per buffer it requires.
@@ -888,18 +861,14 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
 EXPORT_SYMBOL_GPL(vb2_core_reqbufs);
 
 int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
-			 unsigned int flags, unsigned int *count,
+			 unsigned int *count,
 			 unsigned int requested_planes,
 			 const unsigned int requested_sizes[])
 {
 	unsigned int num_planes = 0, num_buffers, allocated_buffers;
 	unsigned plane_sizes[VB2_MAX_PLANES] = { };
-	bool consistent_mem = true;
 	int ret;
 
-	if (flags & V4L2_FLAG_MEMORY_NON_CONSISTENT)
-		consistent_mem = false;
-
 	if (q->num_buffers == VB2_MAX_FRAME) {
 		dprintk(q, 1, "maximum number of buffers already allocated\n");
 		return -ENOBUFS;
@@ -912,15 +881,12 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
 		}
 		memset(q->alloc_devs, 0, sizeof(q->alloc_devs));
 		q->memory = memory;
-		set_queue_consistency(q, consistent_mem);
 		q->waiting_for_buffers = !q->is_output;
 	} else {
 		if (q->memory != memory) {
 			dprintk(q, 1, "memory model mismatch\n");
 			return -EINVAL;
 		}
-		if (!verify_consistency_attr(q, consistent_mem))
-			return -EINVAL;
 	}
 
 	num_buffers = min(*count, VB2_MAX_FRAME - q->num_buffers);
@@ -2581,7 +2547,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
 	fileio->memory = VB2_MEMORY_MMAP;
 	fileio->type = q->type;
 	q->fileio = fileio;
-	ret = vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
+	ret = vb2_core_reqbufs(q, fileio->memory, &fileio->count);
 	if (ret)
 		goto err_kfree;
 
@@ -2638,7 +2604,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
 
 err_reqbufs:
 	fileio->count = 0;
-	vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
+	vb2_core_reqbufs(q, fileio->memory, &fileio->count);
 
 err_kfree:
 	q->fileio = NULL;
@@ -2658,7 +2624,7 @@ static int __vb2_cleanup_fileio(struct vb2_queue *q)
 		vb2_core_streamoff(q, q->type);
 		q->fileio = NULL;
 		fileio->count = 0;
-		vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
+		vb2_core_reqbufs(q, fileio->memory, &fileio->count);
 		kfree(fileio);
 		dprintk(q, 3, "file io emulator closed\n");
 	}

drivers/media/common/videobuf2/videobuf2-dma-contig.c

@@ -42,11 +42,6 @@ struct vb2_dc_buf {
 	struct dma_buf_attachment	*db_attach;
 };
 
-static inline bool vb2_dc_buffer_consistent(unsigned long attr)
-{
-	return !(attr & DMA_ATTR_NON_CONSISTENT);
-}
-
 /*********************************************/
 /*        scatterlist table functions        */
 /*********************************************/
@@ -341,13 +336,6 @@ static int
 vb2_dc_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
 				   enum dma_data_direction direction)
 {
-	struct vb2_dc_buf *buf = dbuf->priv;
-	struct sg_table *sgt = buf->dma_sgt;
-
-	if (vb2_dc_buffer_consistent(buf->attrs))
-		return 0;
-
-	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
 	return 0;
 }
 
@@ -355,13 +343,6 @@ static int
 vb2_dc_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
 				 enum dma_data_direction direction)
 {
-	struct vb2_dc_buf *buf = dbuf->priv;
-	struct sg_table *sgt = buf->dma_sgt;
-
-	if (vb2_dc_buffer_consistent(buf->attrs))
-		return 0;
-
-	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
 	return 0;
 }
 

drivers/media/common/videobuf2/videobuf2-dma-sg.c

@@ -123,8 +123,7 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned long dma_attrs,
 	/*
 	 * NOTE: dma-sg allocates memory using the page allocator directly, so
 	 * there is no memory consistency guarantee, hence dma-sg ignores DMA
-	 * attributes passed from the upper layer. That means that
-	 * V4L2_FLAG_MEMORY_NON_CONSISTENT has no effect on dma-sg buffers.
+	 * attributes passed from the upper layer.
 	 */
 	buf->pages = kvmalloc_array(buf->num_pages, sizeof(struct page *),
 				    GFP_KERNEL | __GFP_ZERO);

drivers/media/common/videobuf2/videobuf2-v4l2.c

@@ -722,22 +722,12 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
 #endif
 }
 
-static void clear_consistency_attr(struct vb2_queue *q,
-				   int memory,
-				   unsigned int *flags)
-{
-	if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP)
-		*flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT;
-}
-
 int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 {
 	int ret = vb2_verify_memory_type(q, req->memory, req->type);
 
 	fill_buf_caps(q, &req->capabilities);
-	clear_consistency_attr(q, req->memory, &req->flags);
-	return ret ? ret : vb2_core_reqbufs(q, req->memory,
-					    req->flags, &req->count);
+	return ret ? ret : vb2_core_reqbufs(q, req->memory, &req->count);
 }
 EXPORT_SYMBOL_GPL(vb2_reqbufs);
 
@@ -769,7 +759,6 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
 	unsigned i;
 
 	fill_buf_caps(q, &create->capabilities);
-	clear_consistency_attr(q, create->memory, &create->flags);
 	create->index = q->num_buffers;
 	if (create->count == 0)
 		return ret != -EBUSY ? ret : 0;
@@ -813,7 +802,6 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
 		if (requested_sizes[i] == 0)
 			return -EINVAL;
 	return ret ? ret : vb2_core_create_bufs(q, create->memory,
-						create->flags,
 						&create->count,
 						requested_planes,
 						requested_sizes);
@@ -998,12 +986,11 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
 	int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
 
 	fill_buf_caps(vdev->queue, &p->capabilities);
-	clear_consistency_attr(vdev->queue, p->memory, &p->flags);
 	if (res)
 		return res;
 	if (vb2_queue_is_busy(vdev, file))
 		return -EBUSY;
-	res = vb2_core_reqbufs(vdev->queue, p->memory, p->flags, &p->count);
+	res = vb2_core_reqbufs(vdev->queue, p->memory, &p->count);
 	/* If count == 0, then the owner has released all buffers and he
 	   is no longer owner of the queue. Otherwise we have a new owner. */
 	if (res == 0)
@@ -1021,7 +1008,6 @@ int vb2_ioctl_create_bufs(struct file *file, void *priv,
 
 	p->index = vdev->queue->num_buffers;
 	fill_buf_caps(vdev->queue, &p->capabilities);
-	clear_consistency_attr(vdev->queue, p->memory, &p->flags);
 	/*
 	 * If count == 0, then just check if memory and type are valid.
 	 * Any -EBUSY result from vb2_verify_memory_type can be mapped to 0.

drivers/media/dvb-core/dvb_vb2.c

@@ -342,7 +342,7 @@ int dvb_vb2_reqbufs(struct dvb_vb2_ctx *ctx, struct dmx_requestbuffers *req)
 
 	ctx->buf_siz = req->size;
 	ctx->buf_cnt = req->count;
-	ret = vb2_core_reqbufs(&ctx->vb_q, VB2_MEMORY_MMAP, 0, &req->count);
+	ret = vb2_core_reqbufs(&ctx->vb_q, VB2_MEMORY_MMAP, &req->count);
 	if (ret) {
 		ctx->state = DVB_VB2_STATE_NONE;
 		dprintk(1, "[%s] count=%d size=%d errno=%d\n", ctx->name,

drivers/media/v4l2-core/v4l2-compat-ioctl32.c

@@ -246,9 +246,6 @@ struct v4l2_format32 {
  * @memory:	buffer memory type
  * @format:	frame format, for which buffers are requested
  * @capabilities: capabilities of this buffer type.
- * @flags:	additional buffer management attributes (ignored unless the
- *		queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability and
- *		configured for MMAP streaming I/O).
  * @reserved:	future extensions
  */
 struct v4l2_create_buffers32 {
@@ -257,8 +254,7 @@ struct v4l2_create_buffers32 {
 	__u32			memory;	/* enum v4l2_memory */
 	struct v4l2_format32	format;
 	__u32			capabilities;
-	__u32			flags;
-	__u32			reserved[6];
+	__u32			reserved[7];
 };
 
 static int __bufsize_v4l2_format(struct v4l2_format32 __user *p32, u32 *size)
@@ -359,8 +355,7 @@ static int get_v4l2_create32(struct v4l2_create_buffers __user *p64,
 {
 	if (!access_ok(p32, sizeof(*p32)) ||
 	    copy_in_user(p64, p32,
-			 offsetof(struct v4l2_create_buffers32, format)) ||
-	    assign_in_user(&p64->flags, &p32->flags))
+			 offsetof(struct v4l2_create_buffers32, format)))
 		return -EFAULT;
 	return __get_v4l2_format32(&p64->format, &p32->format,
 				   aux_buf, aux_space);
@@ -422,7 +417,6 @@ static int put_v4l2_create32(struct v4l2_create_buffers __user *p64,
 	    copy_in_user(p32, p64,
 			 offsetof(struct v4l2_create_buffers32, format)) ||
 	    assign_in_user(&p32->capabilities, &p64->capabilities) ||
-	    assign_in_user(&p32->flags, &p64->flags) ||
 	    copy_in_user(p32->reserved, p64->reserved, sizeof(p64->reserved)))
 		return -EFAULT;
 	return __put_v4l2_format32(&p64->format, &p32->format);

drivers/media/v4l2-core/v4l2-ioctl.c

@@ -2044,6 +2044,9 @@ static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
 
 	if (ret)
 		return ret;
+
+	CLEAR_AFTER_FIELD(p, capabilities);
+
 	return ops->vidioc_reqbufs(file, fh, p);
 }
 
@@ -2083,7 +2086,7 @@ static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,
 	if (ret)
 		return ret;
 
-	CLEAR_AFTER_FIELD(create, flags);
+	CLEAR_AFTER_FIELD(create, capabilities);
 
 	v4l_sanitize_format(&create->format);
 

include/media/videobuf2-core.h

@@ -744,8 +744,6 @@ void vb2_core_querybuf(struct vb2_queue *q, unsigned int index, void *pb);
  * vb2_core_reqbufs() - Initiate streaming.
  * @q:		pointer to &struct vb2_queue with videobuf2 queue.
  * @memory:	memory type, as defined by &enum vb2_memory.
- * @flags:	auxiliary queue/buffer management flags. Currently, the only
- *		used flag is %V4L2_FLAG_MEMORY_NON_CONSISTENT.
  * @count:	requested buffer count.
  *
  * Videobuf2 core helper to implement VIDIOC_REQBUF() operation. It is called
@@ -770,13 +768,12 @@ void vb2_core_querybuf(struct vb2_queue *q, unsigned int index, void *pb);
  * Return: returns zero on success; an error code otherwise.
  */
 int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
-		    unsigned int flags, unsigned int *count);
+		    unsigned int *count);
 
 /**
  * vb2_core_create_bufs() - Allocate buffers and any required auxiliary structs
  * @q: pointer to &struct vb2_queue with videobuf2 queue.
  * @memory: memory type, as defined by &enum vb2_memory.
- * @flags: auxiliary queue/buffer management flags.
  * @count: requested buffer count.
  * @requested_planes: number of planes requested.
  * @requested_sizes: array with the size of the planes.
@@ -794,7 +791,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
  * Return: returns zero on success; an error code otherwise.
  */
 int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
-			 unsigned int flags, unsigned int *count,
+			 unsigned int *count,
 			 unsigned int requested_planes,
 			 const unsigned int requested_sizes[]);
 

include/uapi/linux/videodev2.h

@@ -191,8 +191,6 @@ enum v4l2_memory {
 	V4L2_MEMORY_DMABUF           = 4,
 };
 
-#define V4L2_FLAG_MEMORY_NON_CONSISTENT		(1 << 0)
-
 /* see also http://vektor.theorem.ca/graphics/ycbcr/ */
 enum v4l2_colorspace {
 	/*
@@ -949,10 +947,7 @@ struct v4l2_requestbuffers {
 	__u32			type;		/* enum v4l2_buf_type */
 	__u32			memory;		/* enum v4l2_memory */
 	__u32			capabilities;
-	union {
-		__u32		flags;
-		__u32		reserved[1];
-	};
+	__u32			reserved[1];
 };
 
 /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */
@@ -2456,9 +2451,6 @@ struct v4l2_dbg_chip_info {
  * @memory:	enum v4l2_memory; buffer memory type
  * @format:	frame format, for which buffers are requested
  * @capabilities: capabilities of this buffer type.
- * @flags:	additional buffer management attributes (ignored unless the
- *		queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability
- *		and configured for MMAP streaming I/O).
  * @reserved:	future extensions
  */
 struct v4l2_create_buffers {
@@ -2467,8 +2459,7 @@ struct v4l2_create_buffers {
 	__u32			memory;
 	struct v4l2_format	format;
 	__u32			capabilities;
-	__u32			flags;
-	__u32			reserved[6];
+	__u32			reserved[7];
 };
 
 /*