On Wed, 29 May 2013, Jean Delvare wrote:

I am worried and confused by some Kconfig dependencies in the HID
subsystem.

There are 11 HID device drivers which are defined in drivers/hid/Kconfig
with:

	tristate "..." if EXPERT
	default !EXPERT

Unless EXPERT is enabled (and that's not the default), these driver
entries are hidden and automatically selected. If CONFIG_HID=m, they are
selected as modules. If CONFIG_HID=y, they are built into the kernel. So
it is impossible to have CONFIG_HID=y and build these device drivers as
modules - as device drivers typically are.

I would like to understand the reasoning behind this complexity. What is
so special about these 11 drivers, that we can't just let the (kernel
configuring) user chose if he/she wants them and in what form?

That's quite a old story with some history behind. Linus himself 
originally requested it, then much later asked the same question you did. 
See some background here:

	https://lkml.org/lkml/2010/5/20/227

The thing is, that things indeed have changed quite a bit since then. We 
are no longer in a situation that the generic driver would serve 99.99% of 
the world and the specific drivers would be just quirks.

Wouldn't "default !EXPERT" and a good old "If unsure, say Y" in the help
text be enough?

Normally, yes. This was all introduced back when separating out all the 
messy quirks from generic hid driver into sub-drivers for maintaing 
sort-of backwards compatibility and avoid confusion.

Also I find it unpleasant that this construct completely hides the
option from the user, as if it did not exist, except if other options
depend on it. This is inconsistent and makes it difficult for the user
to know whether a specific kernel version includes a given driver or not
(one has to check .config afterward to know the answer.)

Yes. Again, purely historical reasons.

Put in short, I don't like the way things are today and would welcome
changes in this area.

As things have changed a lot since 2.6.28, we can try to put things more 
in line now for 3.11 or so.

-- 
Jiri Kosina
SUSE Labs