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, 21 deletions

diff --git a/arch/arm/mach-tegra/timer.c b/arch/arm/mach-tegra/timer.c
index e2272d263a83..732c724008b1 100644
--- a/arch/arm/mach-tegra/timer.c
+++ b/arch/arm/mach-tegra/timer.c
@@ -19,7 +19,6 @@
 
 #include <linux/init.h>
 #include <linux/err.h>
-#include <linux/sched.h>
 #include <linux/time.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
@@ -106,25 +105,9 @@ static struct clock_event_device tegra_clockevent = {
         .set_mode       = tegra_timer_set_mode,
 };
 
-static DEFINE_CLOCK_DATA(cd);
-
-/*
- * Constants generated by clocks_calc_mult_shift(m, s, 1MHz, NSEC_PER_SEC, 60).
- * This gives a resolution of about 1us and a wrap period of about 1h11min.
- */
-#define SC_MULT         4194304000u
-#define SC_SHIFT        22
-
-unsigned long long notrace sched_clock(void)
-{
-        u32 cyc = timer_readl(TIMERUS_CNTR_1US);
-        return cyc_to_fixed_sched_clock(&cd, cyc, (u32)~0, SC_MULT, SC_SHIFT);
-}
-
-static void notrace tegra_update_sched_clock(void)
+static u32 notrace tegra_read_sched_clock(void)
 {
-        u32 cyc = timer_readl(TIMERUS_CNTR_1US);
-        update_sched_clock(&cd, cyc, (u32)~0);
+        return timer_readl(TIMERUS_CNTR_1US);
 }
 
 /*
@@ -218,8 +201,7 @@ static void __init tegra_init_timer(void)
                 WARN(1, "Unknown clock rate");
         }
 
-        init_fixed_sched_clock(&cd, tegra_update_sched_clock, 32,
-                               1000000, SC_MULT, SC_SHIFT);
+        setup_sched_clock(tegra_read_sched_clock, 32, 1000000);
 
         if (clocksource_mmio_init(timer_reg_base + TIMERUS_CNTR_1US,
                 "timer_us", 1000000, 300, 32, clocksource_mmio_readl_up)) {