> -----Original Message----- > From: Mauro Carvalho Chehab [mailto:mchehab@xxxxxxxxxxxxx] > Sent: Friday, September 11, 2009 10:34 PM > To: Hiremath, Vaibhav > Cc: Devin Heitmueller; Hans Verkuil; linux-media@xxxxxxxxxxxxxxx > Subject: Re: RFCv2: Media controller proposal > > Em Fri, 11 Sep 2009 21:23:50 +0530 > "Hiremath, Vaibhav" <hvaibhav@xxxxxx> escreveu: > > > > -----Original Message----- > > > From: linux-media-owner@xxxxxxxxxxxxxxx [mailto:linux-media- > > > owner@xxxxxxxxxxxxxxx] On Behalf Of Devin Heitmueller > > > Sent: Friday, September 11, 2009 9:16 PM > > > To: Mauro Carvalho Chehab > > > Cc: Hans Verkuil; linux-media@xxxxxxxxxxxxxxx > > > Subject: Re: RFCv2: Media controller proposal > > > > > > On Fri, Sep 11, 2009 at 11:13 AM, Mauro Carvalho Chehab > > > <mchehab@xxxxxxxxxxxxx> wrote: > > > > Em Thu, 10 Sep 2009 23:35:52 +0200 > > > > Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > > > > > > <snip> > > > > > > > > I was talking not about specific attributes, but about the > V4L2 > > > API controls > > > > that you may eventually need to "hijack" (using that context- > > > sensitive > > > > thread-unsafe approach you described). > > > > > > > > Anyway, by using sysfs, you won't have any thread issues, > since > > > you'll be able > > > > to address each sub-device individually: > > > > > > > > echo 1 >/sys/class/media/mc0/video:dsp0/enable_stats > > > > > > > > > > > > > > > > Cheers, > > > > Mauro > > > > > > Mauro, > > > > > > Please, *seriously* reconsider the notion of making sysfs a > > > dependency > > > of V4L. While sysfs is great for a developer who wants to poke > > > around > > > at various properties from a command line during debugging, it > is an > > > absolute nightmare for any developer who wants to write an > > > application > > > in C that is expected to actually use the interface. The amount > of > > > extra code for all the string parsing alone would be ridiculous > > > (think > > > of how many calls you're going to have to make to sscanf or > atoi). > > > It's so much more straightforward to be able to have ioctl() > calls > > > that can return an actual struct with nice things like > enumeration > > > data types etc. > > The complexity of the interface will greatly depend on the way > things will be > mapped there, and the number of tree levels will be used. Also, as > sysfs > accepts soft links, we may have the same node pointed on different > places. > This can be useful to ek speed. > > In order to have something optimized for application, we can imagine > having, > for example, under /sys/class/media/mc0/subdevs, links to all the > several subdevs, > like: > > video:vin0 > video:vin1 > audio:audio0 > audio:audio1 > dsp:dsp0 > dsp:dsp0 > dvb:adapter0 > i2c:vin0:tvp5150 > ... > > each of them being a link to some specific sysfs node, all of this > created by > V4L2 core, to be sure that all devices will implement it at the > standard way. > > If some parameter should be bind, for example at the video input > device 0, you > just need to write to a node like: > /sys/class/media/mc0/subdevs/attr/<atribute> > > (all the above names are just examples - we'll need to properly > define the > sysfs tree we need to fulfill the requirements). > > Also, it should be noticed that you'll need to use sysfs anyway, to > get subdev's > major/minor numbers and to associate them with a file name under > /dev. > > > > > > > Just my opinion, of course. > > > > > [Hiremath, Vaibhav] Mauro, > > > > Definitely SYSFS interface is a nightmare for the application > developer, and again we have not thought of backward compatibility > here. > > What do you mean by backward compatibility? An application using the > standard > V4L2 API will keep working, but if they'll use the media controller > sysfs, they'll have > extra functionality. > [Hiremath, Vaibhav] I was referring to standard V4L2 interface; I was referring to backward compatibility between Media controller devices itself. Have you thought of custom parameter configuration? For example H3A(20)/Resizer(64) sub-device will have coeff. Which is non-standard (we had some discussion in the past) - With SYSFS approach it is really difficult to pass big parameter to sub-device, which we can easily achieve using IOCTL. Thanks, Vaibhav > I'm not saying that we should use what we currently have, but to use > sysfs to > create standard classes (and/or buses) that fulfill the needs for > media > controller to match the RFC requirements. > > > How application would know/decide on which node is exist and > stuff? Every video board will have his separate way of notions for > creating SYSFS nodes and maintaining standard between them would be > really mess. > > Yes, but none currently have a media controller node. As sysfs > provides links, > we can link the media controller to the old nodes or vice versa (for > the few > devices that already have their proper nodes). > > > There has to be enumeration kind of interface to make standard > application work seamlessly. > > That's for sure. > > > > Cheers, > Mauro -- 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
