On Fri June 28 2013 14:42:46 Mauro Carvalho Chehab wrote: > Em Fri, 28 Jun 2013 13:18:44 +0200 > Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > > > On Fri June 28 2013 13:00:43 Mauro Carvalho Chehab wrote: > > > Em Fri, 28 Jun 2013 10:24:15 +0200 > > > Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > > > > > > > This fixes a dependency problem as found by Randy Dunlap: > > > > > > > > https://lkml.org/lkml/2013/6/27/501 > > > > > > > > Mauro, is there any reason for any V4L2 driver to depend on VIDEO_DEV instead of > > > > just VIDEO_V4L2? > > > > > > > > Some drivers depend on VIDEO_DEV, some on VIDEO_V4L2, some on both. It's all > > > > pretty chaotic. > > > > > > It should be noticed that, despite its name, this config is actually a > > > joint dependency of VIDEO_DEV and I2C that will compile drivers as module > > > if either I2C or VIDEO_DEV is a module: > > > > > > config VIDEO_V4L2 > > > tristate > > > depends on (I2C || I2C=n) && VIDEO_DEV > > > default (I2C || I2C=n) && VIDEO_DEV > > > > > > So, a V4L2 device that doesn't have any I2C device doesn't need to depend > > > on VIDEO_V4L2. That includes, for example, reversed-engineered webcam > > > drivers where the sensor code is inside the driver and a few capture-only > > > device drivers. > > > > Yes, it does have to depend on it. That's exactly why usbtv is failing: like > > any other v4l2 driver usbtv needs the videodev.ko module. That is dependent > > on VIDEO_V4L2. What is happening here is that the dependency of usbtv on > > VIDEO_DEV allows it to be built as part of the kernel, but VIDEO_V4L2 is built > > as a module due to its I2C dependency with the result that usbtv can't link to > > the videodev functions. > > > > The way things are today I do not believe any v4l2 driver should depend on > > VIDEO_DEV, instead they should all depend on VIDEO_V4L2. That would make a > > lot more sense. > > Hmm... > > $ git grep -l i2c drivers/media/v4l2-core/ > drivers/media/v4l2-core/tuner-core.c (not part of videodev.ko module) > drivers/media/v4l2-core/v4l2-async.c > drivers/media/v4l2-core/v4l2-common.c > drivers/media/v4l2-core/v4l2-ctrls.c (actually, there's just a comment there) > drivers/media/v4l2-core/v4l2-device.c > > $ git grep CONFIG_I2C drivers/media/v4l2-core/ > drivers/media/v4l2-core/v4l2-common.c:#if IS_ENABLED(CONFIG_I2C) > drivers/media/v4l2-core/v4l2-common.c:#endif /* defined(CONFIG_I2C) */ > drivers/media/v4l2-core/v4l2-device.c:#if IS_ENABLED(CONFIG_I2C) > > yes, there are some parts of videodev that are dependent on I2C. > > That's basically why all V4L2 drivers should depend on VIDEO_V4L2. > > That's said, before the addition of v4l2-async, it was safe to compile > the core without I2C, as the parts of the code that are I2C specific are > protected by a: > #if defined(CONFIG_I2C) > > With its addition, I suspect that we'll still have Kbuild issues, if I2C > is disabled and a driver that doesn't depends on I2C is compiled. > > So, 2 patches seem to be needed: > > 1) a patch that replaces all driver dependencies from CONFIG_DEV to > CONFIG_V4L2; > > 2) a patch that fixes the issues with v4l2-async. > > With regards to the last one, I can see 3 ways to fix it: > 1) don't add v4l2-async at videodev.ko if I2C is not selected; > 2) protect the I2C specific parts of v4l2-async with > #if defined(CONFIG_I2C) > 3) put v4l2-async on a separate module. > > (or some combination of the above) > > As only very few drivers use v4l2-async, as this is more focused to > fix troubles with OT, I think that the better would be to do (3) and > to add an specific Kconfig entry for it. No, #2 is the right choice here. That's necessary anyway since it is a valid use-case that I2C is disabled and you use it for platform devices only. Guennadi, can you look at this? The only thing that is probably needed is that match_i2c returns false if CONFIG_I2C is undefined. I prefer to keep this part of videodev, at least for now: I think there will be a fairly quick uptake of this API internally, certainly for subdevs. Note BTW that even x86 kernels come with CONFIG_OF enabled these days. 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
