linux-kernel - [136/200] clocksource: sh_tmu: compute mult and shift before registration

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Message-Id: <20100701174257.900362441@clark.site>
Date:	Thu, 01 Jul 2010 10:43:46 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Aurelien Jarno <aurelien@...el32.net>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: [136/200] clocksource: sh_tmu: compute mult and shift before registration

2.6.34-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aurelien Jarno <aurelien@...el32.net>

commit 66f49121ffa41a19c59965b31b046d8368fec3c7 upstream.

Since commit 98962465ed9e6ea99c38e0af63fe1dcb5a79dc25 ("nohz: Prevent
clocksource wrapping during idle"), the CPU of an R2D board never goes
to idle. This commit assumes that mult and shift are assigned before
the clocksource is registered. As a consequence the safe maximum sleep
time is negative and the CPU never goes into idle.

This patch fixes the problem by moving mult and shift initialization
from sh_tmu_clocksource_enable() to sh_tmu_register_clocksource().

Signed-off-by: Aurelien Jarno <aurelien@...el32.net>
Signed-off-by: Paul Mundt <lethal@...ux-sh.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/clocksource/sh_tmu.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

--- a/drivers/clocksource/sh_tmu.c
+++ b/drivers/clocksource/sh_tmu.c
@@ -200,16 +200,8 @@ static cycle_t sh_tmu_clocksource_read(s
 static int sh_tmu_clocksource_enable(struct clocksource *cs)
 {
 	struct sh_tmu_priv *p = cs_to_sh_tmu(cs);
-	int ret;
 
-	ret = sh_tmu_enable(p);
-	if (ret)
-		return ret;
-
-	/* TODO: calculate good shift from rate and counter bit width */
-	cs->shift = 10;
-	cs->mult = clocksource_hz2mult(p->rate, cs->shift);
-	return 0;
+	return sh_tmu_enable(p);
 }
 
 static void sh_tmu_clocksource_disable(struct clocksource *cs)
@@ -229,6 +221,16 @@ static int sh_tmu_register_clocksource(s
 	cs->disable = sh_tmu_clocksource_disable;
 	cs->mask = CLOCKSOURCE_MASK(32);
 	cs->flags = CLOCK_SOURCE_IS_CONTINUOUS;
+
+	/* clk_get_rate() needs an enabled clock */
+	clk_enable(p->clk);
+	/* channel will be configured at parent clock / 4 */
+	p->rate = clk_get_rate(p->clk) / 4;
+	clk_disable(p->clk);
+	/* TODO: calculate good shift from rate and counter bit width */
+	cs->shift = 10;
+	cs->mult = clocksource_hz2mult(p->rate, cs->shift);
+
 	pr_info("sh_tmu: %s used as clock source\n", cs->name);
 	clocksource_register(cs);
 	return 0;


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