Re: [GIT PATCHES] V4L/DVB fixes for 2.6.26

From: Mauro Carvalho Chehab
Date: Sat May 17 2008 - 07:00:40 EST

On Fri, 16 May 2008, Adrian Bunk wrote:

I wanted to simply turn the existing dependencies on INPUT to select's
(and add a dependency on S390 to the "Multimedia devices" menu).

I suspect you're maning depends on !S390. This is not needed, since Multimedia devices is already dependent on HAS_IOMEM.

Yet, I can't imagine any production kernel without INPUT. What happens if INPUT
is disabled? No keyboard, no tablet and no mouse at all?

CONFIG_INPUT is always y unless you enable CONFIG_EMBEDDED.

But on some kinds of embedded systems kernels without INPUT are actually
not uncommon - and they don't have any keyboard or mouse.

There are several embedded V4L/DVB devices: Cellular phones, Set Top Boxes, surveillance systems, etc. I'm not sure if forcing the need for INPUT would be nice. Also, from time to time, people ask for a feature of allowing to disable the IR.

Maybe the better would be to allow the user to explicitly select/unselect IR (for advanced users, and if INPUT). If IR is disabled, we may disable the corresponding <board>-input.c compilation. It doesn't seem hard to do this way, but it will require more time to bake a patch.

I'm not only thinking about today, that's an ongoing problem that could
be fixed this way.

Plus the fact that the dependencies on HOTPLUG don't help you when the
option gets select'ed.

Yes, but the committed patch is adding "depends on HOTPLUG" to all devices that selects FW_LOADER.

If you want, feel free to change this to select, although I can't see any real gain.

Do you have a list of open issues (preferably with .config's)?

The open issue I see is to check the "depends on" for all symbols that are selected.

Should I fix the dependency or can I let VIDEO_IR select I2C and remove

I would remove the select inside VIDEO_IR, adding a separate select for VIDEO_IR_I2C. There's a problem on saa7134-input: It uses some symbols defined on ir-kbd-i2c:

$ grep EXPORT ir-kbd-i2c.c

This breaks saa7134 compilation, if IR-I2C is not selected (or if it is a module, and saa7134 is 'Y).

The proper fix here is to move those symbols to ir-keymaps.c, where the shared IR tables should be.

Except for this, it is safe to allow the user to not compile VIDEO_IR_I2C, even for devices that has i2c IR's. If the module is not compiled, request_module() will fail, but everything else will work properly.

I would add an entry to allow the user to select this explicitly, for power
users, and select it implicitly. Something like:


at the drivers under media/video that selects IR. This need to be mandatory for
a few drivers like saa7134, where some exported symbols at kbd-ir-i2c are used

Are there any real use cases for this justifying adding yet another
twist to the kconfig stuff?

I want to make it simpler, not more complicated, and your last sentence
just describes another new pitfall.

I get the point that it makes sense that it's possible to build only the
one tuner you actually have instead of a dozen automatically select'ed,
but you must somewhere draw a "this twist is not worth the maintainance
overhead" line.

The overall picture is that we cannot add a kconfig option and an
#ifdef around each line of code in the kernel only because someone might
want to disable it.

We simply cannot maintain that in the long term
(drivers/media/ is already at the edge).


And as soon as you enter the 10kB object code size area there are enough
lower hanging fruits for saving space that do not involve increased
complexity in kconfig.

Yes, but in is, in fact, 10K * lots of modules.

The point is that the I2C modules behave very well if they aren't compiled.

I can, for example, compile bttv with just tuner-simple, and nothing else. This will work with all bttv functionalities for two devices I have here. A third analog-only device will require TVAUDIO, otherwise, the audio chip won't be loaded, and audio decoder won't happen. So, the device will work only with video.

I don't see much troubles with most of those I2C helper modules, since the vast majority depends only on I2C (only a few also depends on FW_LOADER).

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