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, 1 insertions, 107 deletions

diff --git a/arch/arm/include/asm/sched_clock.h b/arch/arm/include/asm/sched_clock.h
index c8e6ddf3e860..e3f757263438 100644
--- a/arch/arm/include/asm/sched_clock.h
+++ b/arch/arm/include/asm/sched_clock.h
@@ -8,113 +8,7 @@
 #ifndef ASM_SCHED_CLOCK
 #define ASM_SCHED_CLOCK
 
-#include <linux/kernel.h>
-#include <linux/types.h>
-
-struct clock_data {
-        u64 epoch_ns;
-        u32 epoch_cyc;
-        u32 epoch_cyc_copy;
-        u32 mult;
-        u32 shift;
-};
-
-#define DEFINE_CLOCK_DATA(name) struct clock_data name
-
-static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
-{
-        return (cyc * mult) >> shift;
-}
-
-/*
- * Atomically update the sched_clock epoch.  Your update callback will
- * be called from a timer before the counter wraps - read the current
- * counter value, and call this function to safely move the epochs
- * forward.  Only use this from the update callback.
- */
-static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
-{
-        unsigned long flags;
-        u64 ns = cd->epoch_ns +
-                cyc_to_ns((cyc - cd->epoch_cyc) & mask, cd->mult, cd->shift);
-
-        /*
-         * Write epoch_cyc and epoch_ns in a way that the update is
-         * detectable in cyc_to_fixed_sched_clock().
-         */
-        raw_local_irq_save(flags);
-        cd->epoch_cyc = cyc;
-        smp_wmb();
-        cd->epoch_ns = ns;
-        smp_wmb();
-        cd->epoch_cyc_copy = cyc;
-        raw_local_irq_restore(flags);
-}
-
-/*
- * If your clock rate is known at compile time, using this will allow
- * you to optimize the mult/shift loads away.  This is paired with
- * init_fixed_sched_clock() to ensure that your mult/shift are correct.
- */
-static inline unsigned long long cyc_to_fixed_sched_clock(struct clock_data *cd,
-        u32 cyc, u32 mask, u32 mult, u32 shift)
-{
-        u64 epoch_ns;
-        u32 epoch_cyc;
-
-        /*
-         * Load the epoch_cyc and epoch_ns atomically.  We do this by
-         * ensuring that we always write epoch_cyc, epoch_ns and
-         * epoch_cyc_copy in strict order, and read them in strict order.
-         * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
-         * the middle of an update, and we should repeat the load.
-         */
-        do {
-                epoch_cyc = cd->epoch_cyc;
-                smp_rmb();
-                epoch_ns = cd->epoch_ns;
-                smp_rmb();
-        } while (epoch_cyc != cd->epoch_cyc_copy);
-
-        return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, mult, shift);
-}
-
-/*
- * Otherwise, you need to use this, which will obtain the mult/shift
- * from the clock_data structure.  Use init_sched_clock() with this.
- */
-static inline unsigned long long cyc_to_sched_clock(struct clock_data *cd,
-        u32 cyc, u32 mask)
-{
-        return cyc_to_fixed_sched_clock(cd, cyc, mask, cd->mult, cd->shift);
-}
-
-/*
- * Initialize the clock data - calculate the appropriate multiplier
- * and shift.  Also setup a timer to ensure that the epoch is refreshed
- * at the appropriate time interval, which will call your update
- * handler.
- */
-void init_sched_clock(struct clock_data *, void (*)(void),
-        unsigned int, unsigned long);
-
-/*
- * Use this initialization function rather than init_sched_clock() if
- * you're using cyc_to_fixed_sched_clock, which will warn if your
- * constants are incorrect.
- */
-static inline void init_fixed_sched_clock(struct clock_data *cd,
-        void (*update)(void), unsigned int bits, unsigned long rate,
-        u32 mult, u32 shift)
-{
-        init_sched_clock(cd, update, bits, rate);
-        if (cd->mult != mult || cd->shift != shift) {
-                pr_crit("sched_clock: wrong multiply/shift: %u>>%u vs calculated %u>>%u\n"
-                        "sched_clock: fix multiply/shift to avoid scheduler hiccups\n",
-                        mult, shift, cd->mult, cd->shift);
-        }
-}
-
 extern void sched_clock_postinit(void);
+extern void setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate);
 
 #endif