Re: [PATCHv4 6/8] videobuf2: add queue memory coherency parameter

[Hans Verkuil <hverkuil-cisco@xs4all.nl>]

On 27/07/2021 09:05, Sergey Senozhatsky wrote:
> Preparations for future V4L2_MEMORY_FLAG_NON_COHERENT support.
> 
> Extend vb2_core_reqbufs() parameters list to accept requests'

Extend -> Extend the

> ->flags, which will be used for memory coherency configuration.
> 
> An attempt to allocate a buffer with coherency requirements
> which don't match queue's consistency model will fail.

which don't match -> that do not match the

> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 38 ++++++++++++++++---
>  .../media/common/videobuf2/videobuf2-v4l2.c   |  5 ++-
>  drivers/media/dvb-core/dvb_vb2.c              |  2 +-
>  include/media/videobuf2-core.h                | 10 ++++-
>  4 files changed, 44 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index 55af63d54f23..af4db310cf5e 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -738,11 +738,31 @@ int vb2_verify_memory_type(struct vb2_queue *q,
>  }
>  EXPORT_SYMBOL(vb2_verify_memory_type);
>  
> +static void set_queue_coherency(struct vb2_queue *q, bool coherent_mem)
> +{
> +	q->coherent_mem = 1;

This I do not like: coherent memory is the default, and so I think it will
be more robust if this field is renamed to non_coherent_mem and so coherent
memory will be the default since this field will be cleared initially with
kzalloc.

Basically a similar argument that you used in patch 2/8.

I also think that it improves readability, since non-coherent is the
exceptional case, not the rule, and the field name corresponds with the
V4L2 memory flag name.

I noticed that in v1 of this series it was actually called non_coherent_mem,
and it was changed in v2, actually after some comments from me.

But I changed my mind on that, and I think it makes more sense to go back to
calling this non_coherent_mem.

Regards,

	Hans

> +
> +	if (!vb2_queue_allows_cache_hints(q))
> +		return;
> +	if (!coherent_mem)
> +		q->coherent_mem = 0;
> +}
> +
> +static bool verify_coherency_flags(struct vb2_queue *q, bool coherent_mem)
> +{
> +	if (coherent_mem != q->coherent_mem) {
> +		dprintk(q, 1, "memory coherency model mismatch\n");
> +		return false;
> +	}
> +	return true;
> +}
> +
>  int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> -		     unsigned int *count)
> +		     unsigned int flags, unsigned int *count)
>  {
>  	unsigned int num_buffers, allocated_buffers, num_planes = 0;
>  	unsigned plane_sizes[VB2_MAX_PLANES] = { };
> +	bool coherent_mem = true;
>  	unsigned int i;
>  	int ret;
>  
> @@ -757,7 +777,8 @@ 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)) {
> +	    (q->memory != VB2_MEMORY_UNKNOWN && q->memory != memory) ||
> +	    !verify_coherency_flags(q, coherent_mem)) {
>  		/*
>  		 * We already have buffers allocated, so first check if they
>  		 * are not in use and can be freed.
> @@ -794,6 +815,7 @@ 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_coherency(q, coherent_mem);
>  
>  	/*
>  	 * Ask the driver how many buffers and planes per buffer it requires.
> @@ -878,12 +900,13 @@ 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 *count,
> +			 unsigned int flags, 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 coherent_mem = true;
>  	int ret;
>  
>  	if (q->num_buffers == VB2_MAX_FRAME) {
> @@ -899,11 +922,14 @@ 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;
>  		q->waiting_for_buffers = !q->is_output;
> +		set_queue_coherency(q, coherent_mem);
>  	} else {
>  		if (q->memory != memory) {
>  			dprintk(q, 1, "memory model mismatch\n");
>  			return -EINVAL;
>  		}
> +		if (!verify_coherency_flags(q, coherent_mem))
> +			return -EINVAL;
>  	}
>  
>  	num_buffers = min(*count, VB2_MAX_FRAME - q->num_buffers);
> @@ -2576,7 +2602,7 @@ 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, &fileio->count);
> +	ret = vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
>  	if (ret)
>  		goto err_kfree;
>  
> @@ -2633,7 +2659,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
>  
>  err_reqbufs:
>  	fileio->count = 0;
> -	vb2_core_reqbufs(q, fileio->memory, &fileio->count);
> +	vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
>  
>  err_kfree:
>  	q->fileio = NULL;
> @@ -2653,7 +2679,7 @@ 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, &fileio->count);
> +		vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
>  		kfree(fileio);
>  		dprintk(q, 3, "file io emulator closed\n");
>  	}
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 2fbae9bd7b52..b4f70ddb09b0 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -697,7 +697,7 @@ 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);
> -	return ret ? ret : vb2_core_reqbufs(q, req->memory, &req->count);
> +	return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
>  }
>  EXPORT_SYMBOL_GPL(vb2_reqbufs);
>  
> @@ -772,6 +772,7 @@ 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,
> +						0,
>  						&create->count,
>  						requested_planes,
>  						requested_sizes);
> @@ -974,7 +975,7 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
>  		return res;
>  	if (vb2_queue_is_busy(vdev, file))
>  		return -EBUSY;
> -	res = vb2_core_reqbufs(vdev->queue, p->memory, &p->count);
> +	res = vb2_core_reqbufs(vdev->queue, p->memory, 0, &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)
> diff --git a/drivers/media/dvb-core/dvb_vb2.c b/drivers/media/dvb-core/dvb_vb2.c
> index 6974f1731529..959d110407a4 100644
> --- a/drivers/media/dvb-core/dvb_vb2.c
> +++ b/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, &req->count);
> +	ret = vb2_core_reqbufs(&ctx->vb_q, VB2_MEMORY_MMAP, 0, &req->count);
>  	if (ret) {
>  		ctx->state = DVB_VB2_STATE_NONE;
>  		dprintk(1, "[%s] count=%d size=%d errno=%d\n", ctx->name,
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 66e548268242..7e748cd09b7a 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -504,6 +504,8 @@ struct vb2_buf_ops {
>   * @allow_cache_hints: when set user-space can pass cache management hints in
>   *		order to skip cache flush/invalidation on ->prepare() or/and
>   *		->finish().
> + * @coherent_mem: when cleared queue will attempt to allocate buffers using
> + *		non-coherent memory.
>   * @lock:	pointer to a mutex that protects the &struct vb2_queue. The
>   *		driver can set this to a mutex to let the v4l2 core serialize
>   *		the queuing ioctls. If the driver wants to handle locking
> @@ -583,6 +585,7 @@ struct vb2_queue {
>  	unsigned int			uses_qbuf:1;
>  	unsigned int			uses_requests:1;
>  	unsigned int			allow_cache_hints:1;
> +	unsigned int			coherent_mem:1;
>  
>  	struct mutex			*lock;
>  	void				*owner;
> @@ -748,6 +751,8 @@ 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_MEMORY_FLAG_NON_COHERENT.
>   * @count:	requested buffer count.
>   *
>   * Videobuf2 core helper to implement VIDIOC_REQBUF() operation. It is called
> @@ -772,12 +777,13 @@ 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 *count);
> +		     unsigned int flags, 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.
> @@ -795,7 +801,7 @@ 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 *count,
> +			 unsigned int flags, unsigned int *count,
>  			 unsigned int requested_planes,
>  			 const unsigned int requested_sizes[]);
>  
>