ARM: sched_clock: allow sched_clock to be selected at runtime

sched_clock() is yet another blocker on the road to the single image. This patch implements an idea by Russell King:

http://www.spinics.net/lists/linux-omap/msg49561.html

Instead of asking the platform to implement both sched_clock() itself and the rollover callback, simply register a read() function, and let the ARM code care about sched_clock() itself, the conversion to ns and the rollover. sched_clock() uses this read() function as an indirection to the platform code.

This allow some simplifications and possibly some footprint gain when multiple platforms are compiled in. Among the drawbacks, the removal of the *_fixed_sched_clock optimization which could negatively impact some platforms (sa1100, tegra, versatile and omap).

Tested on 11MPCore, OMAP4 and Tegra.

Quoted 17 lines · Marc Zyngier

sched_clock() is yet another blocker on the road to the single image. This patch implements an idea by Russell King:

http://www.spinics.net/lists/linux-omap/msg49561.html

Instead of asking the platform to implement both sched_clock() itself and the rollover callback, simply register a read() function, and let the ARM code care about sched_clock() itself, the conversion to ns and the rollover. sched_clock() uses this read() function as an indirection to the platform code.

This allow some simplifications and possibly some footprint gain when multiple platforms are compiled in. Among the drawbacks, the removal of the *_fixed_sched_clock optimization which could negatively impact some platforms (sa1100, tegra, versatile and omap).

Quoted 1 line

Tested on 11MPCore, OMAP4 and Tegra.

Great, seems to boot just fine with printk_time :)

I gave it a quick boot test on omap16xx, 2420, 3430, 3630 and 4430:

Tested-by Tony Lindgren <[email protected]>