Hi Hans, On Monday 01 July 2013 16:38:34 Hans Verkuil wrote: > On Mon 1 July 2013 14:42:34 Laurent Pinchart wrote: > > On Monday 24 June 2013 14:48:15 Hans Verkuil wrote: > > > Hi all, > > > > > > While working on extending v4l2-compliance with cropping/selection test > > > cases I decided to add support for that to vivi as well (this would give > > > applications a good test driver to work with). > > > > > > However, I ran into problems how this should be implemented for V4L2 > > > devices (we are not talking about complex media controller devices > > > where the video pipelines are setup manually). > > > > > > There are two problems, one related to ENUM_FRAMESIZES and one to S_FMT. > > > > > > The ENUM_FRAMESIZES issue is simple: if you have a sensor that has > > > several possible frame sizes, and that can crop, compose and/or scale, > > > then you need to be able to set the frame size. > > > > You mentioned that this discussion relates to simple pipelines controlled > > through a video node only. I'd like to take a step back here and first > > define what pipelines we want to support in such a way, and what > > pipelines requires the media controller API. Based on that information we > > can list the use cases we need to support, and then decide on the > > S_FMT/S_SELECTION APIs behaviour. > > It's fairly simple. If I have a video capture device, either using S_STD or > S_DV_TIMINGS to define the resolution of the incoming video, then I can do > cropping, composing and setting the final format without problem. I have all > the information I need to do the calculations. > > On the other hand, replace the video receiver by a sensor or by a software > or hardware image generator that supports a range of resolutions and > everything falls down just because you don't have the equivalent of > S_STD/S_DV_TIMINGS for this type of device. All you need is a way to select > which resolution should be produced at the beginning/source of the video > pipeline. That's exactly why S_STD/S_DV_TIMINGS exist.
I understand that, but it wasn't my point. What I'd like to do is to define what hardware pipelines are supported by pure V4L2 drivers (with a video node only) and what hardware pipelines are supported by a combination of V4L2 and MC. > > I vaguely remember to have discussed this topic previously in a meeting > > but I can't find any related information in my notes at the moment. Would > > anyone happen to have a better memory here ? > > > > > Currently this is decided by S_FMT which maps the format size to the > > > closest valid frame size. This however makes it impossible to e.g. > > > scale up a frame, or compose the image into a larger buffer. > > > > It also makes it impossible to scale a frame down without composing it > > into a larger buffer. That's definitely a bad limitation of the API. > > > > > For video receivers this issue doesn't exist: there the size of the > > > incoming video is decided by S_STD or S_DV_TIMINGS, but no equivalent > > > exists for sensors. > > > > > > I propose that a new selection target is added: V4L2_SEL_TGT_FRAMESIZE. > > > > Just to make sure I understand you correctly, are you proposing a new > > selection target valid on video nodes only, that would control the format > > at the source pad of the sensor ? > > Yes. So this would be valid for an input that: > > - Does not set V4L2_IN_CAP_DV_TIMINGS or CAP_STD in ENUMINPUT > - Does support ENUM_FRAMESIZES And ENUM_FRAMESIZES would then report the list of available FRAMESIZE rectangles, not the list of available output formats ? > > > However, this leads to another problem: the current S_FMT behavior is > > > that it implicitly sets the framesize. That behavior we will have to > > > keep, otherwise applications will start to behave differently. > > > > Which frame size are you talking about ? S_FMT definitely sets the frame > > size in memory, do you mean it also implicitly sets the frame size at the > > sensor source pad ? > > For such devices, yes. How else can you select today which frame size the > sensor should produce? Right, I just wanted to make sure to understand your point properly. > > > I have an idea on how to solve that, but the solution is related to the > > > second problem I found: > > > > > > When you set a new format size, then the compose rectangle must be set > > > to the new format size as well since that has always been the behavior > > > in the past that applications have come to expect. > > > > That's the behaviour applications have come to expect from devices that > > can't compose. From a quick look at the kernel source only Samsung > > devices implement the composition API. Does this behaviour need to be > > preserved there ? > > I believe so. I plan on adding composing capabilities to vivi. Any existing > apps should keep working as expected. Right. My point was that we could possibly break the way S_FMT works for drivers to implement composition, given that existing applications not aware of composition wouldn't work with those drivers anyway. But I wasn't considering drivers upgraded to support composition, which can't break anything. As we need a solution for those, we can as well extend the solution to all drivers. > > > But this makes certain operations impossible to execute: if a driver > > > can't scale, then you can never select a new format size larger than the > > > current (possibly cropped) frame size, even though you would want to > > > compose the unscaled image into such a larger buffer. > > > > > > So what is the behavior that I would expect from drivers? > > > > > > 1) After calling S_STD, S_DV_TIMINGS or > > > S_SELECTION(V4L2_SEL_TGT_FRAMESIZE) the cropping, composing and format > > > parameters are all adjusted to support the new input video size > > > (typically they are all set to the new size). > > > > > > 2) After calling S_CROP/S_SELECTION(CROP) the compose and format > > > parameters are all adjusted to support the new crop rectangle. > > > > > > 3) After calling S_SEL(COMPOSE) the format parameters are adjusted. > > > > > > 4) Calling S_FMT validates the format parameters to support the compose > > > rectangle. > > > > > > However, today step 4 does something different: the compose rectangle > > > will be adjusted to the format size (and in the case of a sensor > > > supporting different framesizes the whole pipeline will be adjusted). > > > > > > The only way I see that would solve this (although it isn't perfect) is > > > to change the behavior of S_FMT only if the selection API was used > > > before by the filehandle. The core can keep easily keep track of that. > > > When the application calls S_FMT and no selection API was used in the > > > past by that filehandle, then the core will call first > > > S_SELECTION(V4L2_SEL_TGT_FRAMESIZE). If that returns -EINVAL, then it > > > will call S_SELECTION(V4L2_SEL_TGT_COMPOSE). Finally it will call S_FMT. > > > Note that a similar sequence is needed for the display case. > > > > > > This means that a driver supporting the selection API can implement the > > > logical behavior and the core will implement the historically-required > > > illogical part. > > > > > > So the fix for this would be to add a new selection target and add > > > compatibility code to the v4l2-core. > > > > > > With that in place I can easily add crop/compose support to vivi. > > > > > > One area of uncertainty is how drivers currently implement S_FMT: do > > > they reset any cropping done before? They should keep the crop rectangle > > > according to the spec (well, it is implied there). Guennadi, what does > > > soc_camera do? > > > > > > Sylwester, I am also looking at exynos4-is/fimc-lite.c. I do see that > > > setting the compose rectangle will adjust it to the format size instead > > > of the other way around, but I can't tell if setting the format size > > > will also adjust the compose rectangle if that is now out-of-bounds of > > > the new format size. > > > > > > Comments? Questions? > > > > How should we handle devices for which supported sizes (crop, compose, > > ...) are restricted by selected pixel format ? > > Good question. ENUM_FRAMESIZES returns the available resolutions dependent > on the pixelformat. That means that when you select a resolution you need > to specify a pixelformat as well. So just a rectangle isn't enough. > > I need to think some more about this. We could first set the pixel format using S_FMT, then proceed to set all resolutions, and finally call S_FMT again as in point 4 above, but that looks a bit like a hack to me. -- Regards, Laurent Pinchart -- 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
