linux-kernel - [PATCH review for 3.18 02/14] watchdog: kempld: fix gcc-4.3 build

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Date:   Mon, 25 Sep 2017 01:14:19 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Guenter Roeck <linux@...ck-us.net>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Subject: [PATCH review for 3.18 02/14] watchdog: kempld: fix gcc-4.3 build

From: Arnd Bergmann <arnd@...db.de>

[ Upstream commit 3736d4eb6af37492aeded7fec0072dedd959c842 ]

gcc-4.3 can't decide whether the constant value in
kempld_prescaler[PRESCALER_21] is built-time constant or
not, and gets confused by the logic in do_div():

drivers/watchdog/kempld_wdt.o: In function `kempld_wdt_set_stage_timeout':
kempld_wdt.c:(.text.kempld_wdt_set_stage_timeout+0x130): undefined reference to `__aeabi_uldivmod'

This adds a call to ACCESS_ONCE() to force it to not consider
it to be constant, and leaves the more efficient normal case
in place for modern compilers, using an #ifdef to annotate
why we do this hack.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 drivers/watchdog/kempld_wdt.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/kempld_wdt.c b/drivers/watchdog/kempld_wdt.c
index d9c1a1601926..e88d1346be5c 100644
--- a/drivers/watchdog/kempld_wdt.c
+++ b/drivers/watchdog/kempld_wdt.c
@@ -140,12 +140,19 @@ static int kempld_wdt_set_stage_timeout(struct kempld_wdt_data *wdt_data,
 					unsigned int timeout)
 {
 	struct kempld_device_data *pld = wdt_data->pld;
-	u32 prescaler = kempld_prescaler[PRESCALER_21];
+	u32 prescaler;
 	u64 stage_timeout64;
 	u32 stage_timeout;
 	u32 remainder;
 	u8 stage_cfg;
 
+#if GCC_VERSION < 40400
+	/* work around a bug compiling do_div() */
+	prescaler = READ_ONCE(kempld_prescaler[PRESCALER_21]);
+#else
+	prescaler = kempld_prescaler[PRESCALER_21];
+#endif
+
 	if (!stage)
 		return -EINVAL;
 
-- 
2.11.0