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, 3 insertions, 14 deletions

diff --git a/arch/arm/mach-picoxcell/time.c b/arch/arm/mach-picoxcell/time.c
index 90a554ff449..6c89cf8ab22 100644
--- a/arch/arm/mach-picoxcell/time.c
+++ b/arch/arm/mach-picoxcell/time.c
@@ -11,7 +11,6 @@
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
-#include <linux/sched.h>
 
 #include <asm/mach/time.h>
 #include <asm/sched_clock.h>
@@ -66,21 +65,11 @@ static void picoxcell_add_clocksource(struct device_node *source_timer)
 	dw_apb_clocksource_register(cs);
 }
 
-static DEFINE_CLOCK_DATA(cd);
 static void __iomem *sched_io_base;
 
-unsigned long long notrace sched_clock(void)
+unsigned u32 notrace picoxcell_read_sched_clock(void)
 {
-	cycle_t cyc = sched_io_base ? __raw_readl(sched_io_base) : 0;
-
-	return cyc_to_sched_clock(&cd, cyc, (u32)~0);
-}
-
-static void notrace picoxcell_update_sched_clock(void)
-{
-	cycle_t cyc = sched_io_base ? __raw_readl(sched_io_base) : 0;
-
-	update_sched_clock(&cd, cyc, (u32)~0);
+	return __raw_readl(sched_io_base);
 }
 
 static const struct of_device_id picoxcell_rtc_ids[] __initconst = {
@@ -100,7 +89,7 @@ static void picoxcell_init_sched_clock(void)
 	timer_get_base_and_rate(sched_timer, &sched_io_base, &rate);
 	of_node_put(sched_timer);
 
-	init_sched_clock(&cd, picoxcell_update_sched_clock, 32, rate);
+	setup_sched_clock(picoxcell_read_sched_clock, 32, rate);
 }
 
 static const struct of_device_id picoxcell_timer_ids[] __initconst = {