linux-kernel - [PATCH 6/9] clocksource: kona: fix get

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Message-Id: <20160810215424.1926658-7-arnd@arndb.de>
Date:	Wed, 10 Aug 2016 23:54:12 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Florian Fainelli <f.fainelli@...il.com>,
	Ray Jui <rjui@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	bcm-kernel-feedback-list@...adcom.com, linux-kernel@...r.kernel.org
Subject: [PATCH 6/9] clocksource: kona: fix get_counter error handling

I could not figure out why, but gcc cannot prove that the
kona_timer_init function always initializes its two outputs,
and we get a warning for the use of the 'lsw' variable later,
which is obviously correct.

drivers/clocksource/bcm_kona_timer.c: In function 'kona_timer_init':
drivers/clocksource/bcm_kona_timer.c:119:13: error: 'lsw' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Slightly reordering the loop makes the warning disappear, after
it becomes more obvious to the compiler that the loop is
always entered on the first iteration.

As pointed out by Ray Jui, there is a related problem in the
way we deal with the loop running into the limit, as we just
keep going there with an invalid counter data, so instead we
now propagate a -ETIMEDOUT result to the caller.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Link: https://patchwork.kernel.org/patch/9174261/
---
Originally sent this as a warning fix only on June 13, this
version actually fixes the incorrect data problem.
---
 drivers/clocksource/bcm_kona_timer.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/clocksource/bcm_kona_timer.c b/drivers/clocksource/bcm_kona_timer.c
index 7e3fd375a627..92f6e4deee74 100644
--- a/drivers/clocksource/bcm_kona_timer.c
+++ b/drivers/clocksource/bcm_kona_timer.c
@@ -66,10 +66,10 @@ static void kona_timer_disable_and_clear(void __iomem *base)
 
 }
 
-static void
+static int
 kona_timer_get_counter(void __iomem *timer_base, uint32_t *msw, uint32_t *lsw)
 {
-	int loop_limit = 4;
+	int loop_limit = 3;
 
 	/*
 	 * Read 64-bit free running counter
@@ -83,18 +83,19 @@ kona_timer_get_counter(void __iomem *timer_base, uint32_t *msw, uint32_t *lsw)
 	 *      if new hi-word is equal to previously read hi-word then stop.
 	 */
 
-	while (--loop_limit) {
+	do {
 		*msw = readl(timer_base + KONA_GPTIMER_STCHI_OFFSET);
 		*lsw = readl(timer_base + KONA_GPTIMER_STCLO_OFFSET);
 		if (*msw == readl(timer_base + KONA_GPTIMER_STCHI_OFFSET))
 			break;
-	}
+	} while (--loop_limit);
 	if (!loop_limit) {
 		pr_err("bcm_kona_timer: getting counter failed.\n");
 		pr_err(" Timer will be impacted\n");
+		return -ETIMEDOUT;
 	}
 
-	return;
+	return 0;
 }
 
 static int kona_timer_set_next_event(unsigned long clc,
@@ -112,8 +113,11 @@ static int kona_timer_set_next_event(unsigned long clc,
 
 	uint32_t lsw, msw;
 	uint32_t reg;
+	int ret;
 
-	kona_timer_get_counter(timers.tmr_regs, &msw, &lsw);
+	ret = kona_timer_get_counter(timers.tmr_regs, &msw, &lsw);
+	if (ret)
+		return ret;
 
 	/* Load the "next" event tick value */
 	writel(lsw + clc, timers.tmr_regs + KONA_GPTIMER_STCM0_OFFSET);
-- 
2.9.0