ARM: 7205/2: 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.
If the platform doesn't provide a read(), the code falls back
to the jiffy counter (just like the default sched_clock).

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.

Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: Eric Miao <eric.y.miao@gmail.com>
Cc: Colin Cross <ccross@android.com>
Cc: Erik Gilling <konkers@android.com>
Cc: Olof Johansson <olof@lixom.net>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Alessandro Rubini <rubini@unipv.it>
Cc: STEricsson <STEricsson_nomadik_linux@list.st.com>
Cc: Lennert Buytenhek <kernel@wantstofly.org>
Cc: Ben Dooks <ben-linux@fluff.org>
Tested-by: Jamie Iles <jamie@jamieiles.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Krzysztof Halasa <khc@pm.waw.pl>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 4 insertions, 16 deletions

diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
index 9edcd520510f..6eeff0e0ae01 100644
--- a/arch/arm/mach-omap2/timer.c
+++ b/arch/arm/mach-omap2/timer.c
@@ -254,7 +254,6 @@ static struct omap_dm_timer clksrc;
 /*
  * clocksource
  */
-static DEFINE_CLOCK_DATA(cd);
 static cycle_t clocksource_read_cycles(struct clocksource *cs)
 {
         return (cycle_t)__omap_dm_timer_read_counter(&clksrc, 1);
@@ -268,23 +267,12 @@ static struct clocksource clocksource_gpt = {
         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
-static void notrace dmtimer_update_sched_clock(void)
+static u32 notrace dmtimer_read_sched_clock(void)
 {
-        u32 cyc;
-
-        cyc = __omap_dm_timer_read_counter(&clksrc, 1);
-
-        update_sched_clock(&cd, cyc, (u32)~0);
-}
-
-unsigned long long notrace sched_clock(void)
-{
-        u32 cyc = 0;
-
         if (clksrc.reserved)
-                cyc = __omap_dm_timer_read_counter(&clksrc, 1);
+                return __omap_dm_timer_read_counter(clksrc.io_base, 1);
 
-        return cyc_to_sched_clock(&cd, cyc, (u32)~0);
+        return 0;
 }
 
 /* Setup free-running counter for clocksource */
@@ -301,7 +289,7 @@ static void __init omap2_gp_clocksource_init(int gptimer_id,
 
         __omap_dm_timer_load_start(&clksrc,
                         OMAP_TIMER_CTRL_ST | OMAP_TIMER_CTRL_AR, 0, 1);
-        init_sched_clock(&cd, dmtimer_update_sched_clock, 32, clksrc.rate);
+        setup_sched_clock(dmtimer_read_sched_clock, 32, clksrc.rate);
 
         if (clocksource_register_hz(&clocksource_gpt, clksrc.rate))
                 pr_err("Could not register clocksource %s\n",