Hi, On Mon, Aug 22, 2011 at 23:31, Hans Verkuil <hverkuil@xxxxxxxxx> wrote: > On Monday, August 22, 2011 19:21:18 Laurent Pinchart wrote: >> Hi Hans, >> >> On Monday 22 August 2011 17:52:12 Hans Verkuil wrote: >> > On Monday, August 22, 2011 17:42:36 Laurent Pinchart wrote: >> > > On Monday 22 August 2011 15:54:03 Guennadi Liakhovetski wrote: >> > > > 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. >> > > >> > > Sakari is on holidays this week. >> > > >> > > > 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. >> > > > Sounds good, just one question: we deliberately don't want to allow CREATE_BUFS to adjust the format in any way, as S_FMT could? >> > > > 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. >> > > What part would be passed down to drivers? Please see my example below. I actually feel the drivers would become slightly simpler with this change. >> > > How much common code would be pushed down to drivers ? I don't think this >> > > is a real issue. I like Pawel's proposal of removing .queue_setup() >> > > better. >> > >> > I still don't see what removing queue_setup will solve or improve. >> >> It will remove handling of the format in vb2 (even if it's a pass-through >> operation). I think it would be cleaner that way. It will also avoid going >> back and forth between drivers and vb2, which would improve code readability. > > I very much doubt it will be more readable or cleaner. For one thing it is > inconsistent with the other ioctl ops where you just call a vb2 function to > handle it. Suddenly here you have to do lots of things to make it work. > This flow: REQBUFS->driver_reqbufs()->vb2_reqbufs()->queue_setup(fmt=NULL, nums, sizes)->vb2_reqbufs->driver_reqbufs CREATE_BUFS->driver_create_bufs()->vb2_create_bufs(fmt)->queue_setup(fmt, nums, sizes)->vb2_create_bufs->driver_create_bufs is more complicated than this flow: REQBUFS->driver_reqbufs()->vb2_reqbufs(nums, sizes)->driver_reqbufs CREATE_BUFS->driver_create_bufs()->vb2_create_bufs(nums, sizes)->driver_create_bufs without giving any clear advantage (at least from what I can see), apart from making Guennadi's change simpler. Below is what I'm proposing. This, in my opinion, makes vb2's interface cleaner, as the format is never passed to it. I don't see what code it'd be passing down to drivers. The goal is to pass (return) nums/sizes to vb2 anyway. Existing queue_setup() could with some modifications become figure_out_params(): driver_create_bufs(create) /* optional */ { /* use create->fmt to figure out num_* and *_sizes */ figure_out_params(create->fmt, &num_buffers, &num_planes, &buf_sizes, &plane_sizes); return vb2_create_bufs(num_buffers, num_planes, buf_sizes, plane_sizes, alloc_ctxs); } driver_reqbufs() { /* use current format to figure out num_* and *_sizes */ figure_out_params(current_fmt, &num_buffers, &num_planes, &buf_sizes, &plane_sizes); return vb2_reqbufs(num_buffers, num_planes, buf_sizes, plane_sizes, alloc_ctxs); } /* ---------- */ vb2_reqbufs(num_buffers, num_planes, buf_sizes, plane_sizes, alloc_ctxs) { if (buffers_allocated) free_buffers(...); return vb2_create_bufs(num_buffers, num_planes, buf_sizes, plane_sizes, alloc_ctxs); } >> > I'd say leave it as it is to keep the diff as small as possible and someone >> > can always attempt to remove it later. Removing queue_setup is independent >> > from multi-size videobuffer management and we should not mix the two. >> >> Guennadi's patch will (at least in my opinion) be cleaner if built on top of >> queue_setup() removal. > > Really? Just adding a single v4l2_format pointer is less clean than removing > queue_setup? That would really surprise me. > Anyway, let Guennadi choose what is easiest. It's an implementation detail in > the end and I just want to get this functionality in. I'm not completely opposed to your last suggestion. I agree the patch would be much shorter. Your proposal is reasonable and simple enough. I just feel that it'd pay off to put a little bit more effort to make the changes I'm proposing, to make the interface cleaner and simplify ping-ponging calls and parameters between drivers and vb2. But I don't mind if we make it simple for now. As you suggested, I'll be more than happy to look into removing queue_setup later. -- Best regards, Pawel Osciak -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
