We discussed a bit more with Hans on IRC, and below is my attempt of a summary. Hans, please, correct me, if I misunderstood anything. Pawel, Sakari, Laurent: please, reply, whether you're ok with this.
On Mon, 22 Aug 2011, Hans Verkuil wrote: > On Monday, August 22, 2011 12:40:25 Guennadi Liakhovetski wrote: [snip] > > It would be good if you also could have a look at my reply to this Pawel's > > mail: > > > > http://article.gmane.org/gmane.linux.drivers.video-input- > infrastructure/36905 > > > > and, specifically, at the vb2_parse_planes() function in it. That's my > > understanding of what would be needed, if we preserve .queue_setup() and > > use your last suggestion to include struct v4l2_format in struct > > v4l2_create_buffers. > > vb2_parse_planes can be useful as a utility function that 'normal' drivers > can > call from the queue_setup. But vb2 should not parse the format directly, it > should just pass it on to the driver through the queue_setup function. > > You also mention: "All frame-format fields like fourcc code, width, height, > colorspace are only input from the user. If the user didn't fill them in, > they > should not be used." > > I disagree with that. The user should fill in a full format description, just > as with S/TRY_FMT. That's the information that the driver will use to set up > the buffers. It could have weird rules like: if the fourcc is this, and the > size is less than that, then we can allocate in this memory bank. > > It is also consistent with REQBUFS: there too the driver uses a full format > (i.e. the last set format). > > I would modify queue_setup to something like this: > > int (*queue_setup)(struct vb2_queue *q, struct v4l2_format *fmt, > unsigned int *num_buffers, > unsigned int *num_planes, unsigned int sizes[], > void *alloc_ctxs[]); > > Whether fmt is left to NULL in the reqbufs case, or whether the driver has to > call g_fmt first before calling vb2 is something that could be decided by > what > is easiest to implement. 1. VIDIOC_CREATE_BUFS passes struct v4l2_create_buffers from the user to the kernel, in which struct v4l2_format is embedded. The user _must_ fill in .type member of struct v4l2_format. For .type == V4L2_BUF_TYPE_VIDEO_CAPTURE or V4L2_BUF_TYPE_VIDEO_OUTPUT .fmt.pix is used, for .type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE or V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE .fmt.pix_mp is used. In both these cases the user _must_ fill in .width, .height, .pixelformat, .field, .colorspace by possibly calling VIDIOC_G_FMT or VIDIOC_TRY_FMT. The user also _may_ optionally fill in any further buffer-size related fields, if it believes to have any special requirements to them. On a successful return from the ioctl() .count and .index fields are filled in by the kernel, .format stays unchanged. The user has to call VIDIOC_QUERYBUF to retrieve specific buffer information. 2. Videobuf2 drivers, that implement .vidioc_create_bufs() operation, call vb2_create_bufs() with a pointer to struct v4l2_create_buffers as a second argument. vb2_create_bufs() in turn calls the .queue_setup() driver callback, whose prototype is modified as follows: int (*queue_setup)(struct vb2_queue *q, const struct v4l2_format *fmt, unsigned int *num_buffers, unsigned int *num_planes, unsigned int sizes[], void *alloc_ctxs[]); with &create->format as a second argument. As pointed out above, this struct is not modified by V4L, instead, the usual arguments 3-6 are filled in by the driver, which are then used by vb2_create_bufs() to call __vb2_queue_alloc(). 3. vb2_reqbufs() shall call .queue_setup() with fmt == NULL, which will be a signal to the driver to use the current format. 4. We keep .queue_setup(), because its removal would inevitably push a part of the common code from vb2_reqbufs() and vb2_create_bufs() down into drivers, thus creating code redundancy and increasing its complexity. You have 24 hours to object, before I proceed with the next version;-) Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
