[PATCH 00/15] mach/io.h cleanup and removal

On Tuesday 14 February 2012, Rob Herring wrote:

quoted

I agree that this is the ideal, but as far as I can tell, we have a
significant amount of functions that are defined in platform specific
code but used in platform specific drivers. E.g. when you have a
piece of code dealing with system management registers in your platform,
that would be used in the cpufreq, irqchip, watchdog and more drivers.

From my quick survey, those categories are really the exception. I would
guess platform_data structs is at least half of it. Older platforms seem
to be another big chunk.

Good to hear. We can certainly take care of the platform data by moving
it to include/linux/platform_data/*.h and the older platforms can
usually keep exporting their header files because we won't get them
to build into the same kernel with other platforms.

Lack of a common usb phy infrastructure is another example of custom
platform functions (tegra usb_phy.h).

Good point.

quoted

* Any symbol that is required to be visible in device drivers
gets declared in arch/arm/include/mach-*/*.h, but we are very
careful about adding only the absolute minimum here.

Why not include/linux? Any includes for drivers which are either
multiple arches (ahci_platform.h) or multiple ARM machines
(linux/amba/pl061.h) are already there. Every platform trying to dump
dozens of includes there would certainly get attention and force some
clean-up.

I strongly believe that any header file should be as localized as possible:

a) no header, all declarations in the one file using it
b) header file in local directory
c) header file in per-platform directory
d) header file in per-architecture directory
e) global header file

We need to get rid of category c in order to make cross-platform kernels
work. Ideally we would move everything into categories a and b, which is
often possible, but for those cases where it doesn't work the logical step
is to have it in arch specific code, not global.

	Arnd