linux-kernel - [PATCH] [media] zl10353: use div_u64 instead of do

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Message-Id: <1455287246-3540549-1-git-send-email-arnd@arndb.de>
Date:	Fri, 12 Feb 2016 15:27:18 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] [media] zl10353: use div_u64 instead of do_div

I noticed a build error in some randconfig builds in the zl10353 driver:

dvb-frontends/zl10353.c:138: undefined reference to `____ilog2_NaN'
dvb-frontends/zl10353.c:138: undefined reference to `__aeabi_uldivmod'

The problem can be tracked down to the use of -fprofile-arcs (using
CONFIG_GCOV_PROFILE_ALL) in combination with CONFIG_PROFILE_ALL_BRANCHES
on gcc version 4.9 or higher, when it fails to reliably optimize
constant expressions.

Using div_u64() instead of do_div() makes the code slightly more
readable by both humans and by gcc, which gives the compiler enough
of a break to figure it all out.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/media/dvb-frontends/zl10353.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/media/dvb-frontends/zl10353.c b/drivers/media/dvb-frontends/zl10353.c
index ef9764a02d4c..160c88710553 100644
--- a/drivers/media/dvb-frontends/zl10353.c
+++ b/drivers/media/dvb-frontends/zl10353.c
@@ -135,8 +135,7 @@ static void zl10353_calc_nominal_rate(struct dvb_frontend *fe,
 
 	value = (u64)10 * (1 << 23) / 7 * 125;
 	value = (bw * value) + adc_clock / 2;
-	do_div(value, adc_clock);
-	*nominal_rate = value;
+	*nominal_rate = div_u64(value, adc_clock);
 
 	dprintk("%s: bw %d, adc_clock %d => 0x%x\n",
 		__func__, bw, adc_clock, *nominal_rate);
@@ -163,8 +162,7 @@ static void zl10353_calc_input_freq(struct dvb_frontend *fe,
 		if (ife > adc_clock / 2)
 			ife = adc_clock - ife;
 	}
-	value = (u64)65536 * ife + adc_clock / 2;
-	do_div(value, adc_clock);
+	value = div_u64((u64)65536 * ife + adc_clock / 2, adc_clock);
 	*input_freq = -value;
 
 	dprintk("%s: if2 %d, ife %d, adc_clock %d => %d / 0x%x\n",
-- 
2.7.0