linux-kernel - [PATCH 1/3] watchdog: kempld: fix gcc-4.3 build

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Date:   Wed,  1 Mar 2017 10:15:29 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Wim Van Sebroeck <wim@...ana.be>, linux-watchdog@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 1/3] watchdog: kempld: fix gcc-4.3 build

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>
---
 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 73c46b3a09ab..2f3b049ea301 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;
 
-- 
2.9.0