On Mon 1 July 2013 14:42:34 Laurent Pinchart wrote: > Hi Hans, > > 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 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 > > 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? > > 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. > > 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. Regards, Hans -- 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
