On Thursday, October 06, 2011 09:09:26 Hans Verkuil wrote: > On Thursday, October 06, 2011 02:32:33 Mauro Carvalho Chehab wrote: > > Em 05-10-2011 20:14, Sakari Ailus escreveu: > > > Hi Mauro, > > > > > > On Wed, Oct 05, 2011 at 06:41:27PM -0300, Mauro Carvalho Chehab wrote: > > >> Em 05-10-2011 17:08, Laurent Pinchart escreveu: > > > [clip] > > >>> The pad-level API doesn't replace the V4L2 API, it complements it. I'm of > > >>> course not advocating modifying any driver to replace V4L2 ioctls by direct > > >>> subdev access. However, the pad-level API needs to be exposed to userspace, as > > >>> some harware simply can't be configured through a video node only. > > >>> > > >>> As Hans also mentionned in his reply, the pad-level API is made of two parts: > > >>> an in-kernel API made of subdev operations, and a userspace API accessed > > >>> through ioctls. As the userspace API is needed for some devices, the kernel > > >>> API needs to be implemented by drivers. We should phase out the non pad-level > > >>> format operations in favor of pad-level operations, as the former can be > > >>> implemented using the later. That has absolutely no influence on the userspace > > >>> API. > > >> > > >> What I'm seeing is that: > > >> - the drivers that are implementing the MC/pad API's aren't > > >> compatible with generic V4L2 applications; > > > > > > This is currently true up to a certain degree; you'll need to configure such > > > devices using media-ctl at least. Even then, such embedded systems do often > > > have automatic exposure and white balance algorithms above the V4L2 (often > > > proprietary implementations). > > > > > > To be really useful for a regular user, such algorithms would also be > > > needed. > > > > > > The two problems are separate but they still both need to be resolved to be > > > able to use general purpose V4L2 applications on such systems in a > > > meaningful way. > > > > That's true, and the MC/pad API's were added to offer support for those proprietary > > plugins via libv4l. > > > > That's fine, but the thing is that some developers seem to think that only the streaming > > should be done via the V4L2 API, and all the rest via pad configs, while others have > > different views. > > The original design always assumed that there would be a default initial setup > that would allow the use of e.g. tvtime to get at least some sort of halfway > decent video from the device. Unfortunately, that never materialized :-( > > > Also, I couldn't see a consense about input selection on drivers that > > implement MC: they could either implement S_INPUT, create one V4L device node for each > > input, or create just one devnode and let userspace (somehow) to discover the valid > > inputs and set the pipelines via MC/pad. > > I don't follow. I haven't seen any MC driver yet that uses S_INPUT as that > generally doesn't make sense. But for a device like tvp5150 we probably need > it since the tvp5150 has multiple inputs. This is actually an interesting > challenge how to implement this as this is platform-level knowledge. I suspect > that the only way to do this that is sufficiently generic is to model this > with MC links. > > > With all those complex and different scenarios, writing a generic plugin/application > > that would cover all possible alternatives with a mix of V4L/MC/pad API's would be > > extremely complex, and will take years to do it right. > > I suspect so as well. > > > In other words, we need to confine the possible solutions to the ones that will > > actually be supported. > > Yes. > > > >> - there's no way to write a generic application that works with all > > >> drivers, even implementing MC/pad API's there as each driver is taking different > > >> a approach on how to map things at the different API's, and pipeline configuration > > >> is device-dependent; > > > > > > The pipeline configuration is device specific but the interfaces are not. > > > Thus it's possible to write a generic plugin which configures the device. > > > > > > The static configuration can be kept in a text file in the first phase and > > > later on hints may be added for synamic configuration on e.g. where digital > > > gain, scaling and cropping should be performed and which resolutions to > > > advertise in enum_framesizes. > > > > Assuming that all drivers do the same, this would be an alternative for such > > plugin. > > > > > But we do not have such plugin yet. > > > > As several SoC developers showed on all opportunities we've met, the complexity > > for those devices is very high. The practical effect of adding a kernel driver > > without the corresponding required library support is that we ended by > > merging incomplete drivers and nobody, except for the manufacturers/developers > > whose submitted them could actually make an userspace application to work > > with. That would be ok if the drivers would be at /staging, but they aren't. > > This situation should be fixed as soon as possible. > > > > I'm seriously considering to not send the patches we have on our tree for those > > drivers upstream while we don't have a solution for that. > > I think that's a bit overkill, I would go with not accepting new submissions > until this is sorted. Just my opinion, though. > > > >> - there's no effort to publish patches to libv4l to match the changes > > >> at the kernel driver. > > > > > > I'd prefer concentrating all efforts towards a single, generic plugin. As > > > noted before, a plugin for OMAP 3 ISP exists, but I don't think it does > > > anything a generic plugin couldn't do, so it hasn't been merged. > > > > > > I'm working on patches to move the text-based pipeline configuration to > > > libmediactl and libv4l2subdev and will post them to the list in the coming > > > few days, among with a few other improvements. This is one of the first > > > required steps towards such generic plugin. > > All these libraries are on Laurent's site. Can we please move it to linuxtv? > > Mauro, wouldn't it be a good idea to create a media-utils.git and merge > v4l-utils, dvb-apps and these new media utils/libs in there? > > > That would be great, but it won't solve, as more mess is being proposed each > > day. One thing is to set the pipelines. Another thing is to not support > > things like S_FMT/S_STD/... ioctl's. The user knows what format he wants, > > and that's what S_FMT/S_STD tells to the driver. the extra formats at the > > pipeline could be handled by a policy either at the driver or at a libv4l, > > although I don't think that a generic libv4l plugin would be capable of > > doing it (see more about that bellow). > < > > > Unfortunately I haven't been able to use much of my time on this; help would > > > indeed be appreciated from any interested party. > > > > > > [clip] > > > > > >> I'm fine on providing raw interfaces, just like we have for some types of device > > >> (like the block raw interfaces used by CD-ROM drivers) as a bonus, but this should > > >> never replace an API where an application developed by a third party could work > > >> with all media hardware, without needing hardware specific details. > > > > > > I agree. > > > > > > [clip] > > > > > >>>>>> If the application wants a different image resolution, it will use > > >>>>>> S_FMT. In this case, what userspace expects is that the driver will > > >>>>>> scale, if supported, or return -EINVAL otherwise. > > >>>>> > > >>>>> With the OMAP3 ISP, which is I believe what Javier was asking about, the > > >>>>> application will set the format on the OMAP3 ISP resizer input and output > > >>>>> pads to configure scaling. > > >>>> > > >>>> The V4L2 API doesn't tell where a function like scaler will be implemented. > > >>>> So, it is fine to implement it at tvp5151 or at the omap3 resizer, when a > > >>>> V4L2 call is sent. > > >>> > > >>> By rolling a dice ? :-) > > >> > > >> By using good sense. I never had a case where I had doubts about where the > > >> scaling should be implemented on the drivers I've coded. For omap3/tvp5151, the > > >> decision is also clear: it should be done at the bridge (omap3) resizer, as the > > >> demod doesn't support scaling. > > > > > > Good sense in this case would require knowledge of the tv tuner in the > > > camera ISP driver. One could also, and actually does, connect sensors which > > > can do scaling in two steps to the same ISP. How does the ISP driver now > > > know where to do scaling? > > > > Does it actually make sense to allow scaling on both? In the case of the > > generic plugin you're writing, would it do scale on both? If not, how > > would it decide where to scale? Moving the problem to userspace won't solve > > it, and would require userspace to take some hard decisions based on the specific > > hardware designs. In practice, it means that, every time a hardware is updated > > (a new sensor is added, etc), both the plugin and the driver will need to be > > touched, at the same time. This also means that the userspace plugin will > > be dependent on an specific kernel version, which would be a real mess to > > the distributors to package the libv4l plugin. > > > > Btw, we have some devices that support scaling on both tv decoder and bridge. > > As not all tv decoders have scaling, the decision were to implement scaling > > it only at the bridge. This was as good as doing it at the sensor (or even > > better, as some bridges have temporal/spacial decimation filtering, with > > provides a better decimation than a pure spacial filtering, and can reduce > > the quantization noise). > > The subdevs still need to support scaling since there are bridges that do > not do any scaling (e.g. the Conexant bridges in ivtv and cx18). > > > > OMAP 3 ISP as such is a relatively simple one; there are ISPs which have two > > > scalers and ability to write the image to memory also in between the two. > > > > > > I don't think a driver, be that tv tuner / sensor or ISP driver, has enough > > > information to perform the pipeline configuration which is mandatory to > > > implement the standard V4L2 ioctls for e.g. format setting and cropping. We > > > actually had such an implementation of the OMAP 3 ISP driver around 2009 > > > (but without MC or V4L2 subdevs, still the underlying technical issues are > > > the same) and it was a disaster. The patches were posted to linux-media a > > > few times back then if you're interested. It was evident something had to be > > > done, and now we have the Media controller and V4L2 subdev user space APIs. > > > > As I said before, you're just transfering the problem from the kernel to > > something else, without actually solving it. > > I agree with Mauro here. The reason it was a disaster in the omap driver is > that they tried to use the V4L2 API as the main API. That truly doesn't work. > But what I want to see is just an initial default pipeline that allows you > to test video with a standard application. Nothing fancy. That should be > easy on omap3: you have effectively three inputs (two serial, one parallel), > and you can create a default pipeline from there. Once userspace starts > manually messing around with the pipeline you can drop support it, that's > fine by me. > > Whether or not you include a scaler in the default pipeline is optional > as far as I am concerned. > > I fear that plugins just don't cut it. And even if they do, that it will be > very easy for the plugin and the corresponding driver to go out of sync. > > Note that we could well have both: a simple default pipeline, and a more > complex plugin that gives more functionality/better quality. > > But I remain very skeptical about having just a plugin. I want to add one more thing: right now the MC is only used on specialized hardware, but I'm sure we will start to see such SoC devices on laptops, etc. in the future running generic linux distros. There we will need to support generic applications as well. 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
