On Friday 29 August 2014 20:05:49 Bartlomiej Zolnierkiewicz wrote:

I've been looking lately into making it possible to easily go
from multi_v7_defconfig config to a single platform one (in my
case Exynos one) and removing the need to keep the latter (i.e.
exynos_defconfig) in the kernel tree in the long-term.

Because of this I've noticed that some config options for platform
specific hardware that are selected in multi_v7_defconfig don't
have proper dependencies.  This results in more complex than
necessary single platform configs (obtained from a multiplatform
config) and unnecessarily bigger resulting kernel images.

Your patch also adds/uncovers some such config options.

Lets first look at sizes of resulting vmlinux images for single
platform Exynos config before and after your patch:

  $ size vmlinux.*
     text    data     bss     dec     hex filename
  7817317  517188  278992 8613497  836e79 vmlinux.before
  7978325  527012  279056 8784393  860a09 vmlinux.after

  (=> the patch results in 170kB bigger vmlinux size)

Interesting work. We don't currently have a policy for this,
so we should first talk about whether the behavior that you
want is desirable. The alternative would be that everybody
who wants to build a platform-specific kernel out of
multi_v7_defconfig has to go through the extra work of not
only disabling the platforms but also the individual drivers
for the other platforms.

This is a bit tricky for drivers that may be shared between
a few platforms in multi_v7_defconfig but are meaningless
on the others. We could solve that by having more complex
dependencies for each of those drivers, but that is where
maintaining those gets really messy.

A related problem that I think is more significant is that
some platforms 'select' a particular driver and when you
disable the platform, that driver is suddenly removed from the
defconfig for all other platforms as well. This has bitten
us a few times in the past, and I'd really like to fix those
cases first.

	Arnd