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From: (Ian Abbott)
Subject: [PATCH] staging: comedi: dt3000: Fix rounding up of timer divisor
Date: Mon, 12 Aug 2019 13:08:14 +0100
Message-ID: <> (raw)

`dt3k_ns_to_timer()` determines the prescaler and divisor to use to
produce a desired timing period.  It is influenced by a rounding mode
and can round the divisor up, down, or to the nearest value.  However,
the code for rounding up currently does the same as rounding down!  Fix
ir by using the `DIV_ROUND_UP()` macro to calculate the divisor when
rounding up.

Also, change the types of the `divider`, `base` and `prescale` variables
from `int` to `unsigned int` to avoid mixing signed and unsigned types
in the calculations.

Also fix a typo in a nearby comment: "improvment" => "improvement".

Signed-off-by: Ian Abbott <abbotti at>
 drivers/staging/comedi/drivers/dt3000.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/comedi/drivers/dt3000.c b/drivers/staging/comedi/drivers/dt3000.c
index 2edf3ee91300..8621e3833ad5 100644
--- a/drivers/staging/comedi/drivers/dt3000.c
+++ b/drivers/staging/comedi/drivers/dt3000.c
@@ -342,9 +342,9 @@ static irqreturn_t dt3k_interrupt(int irq, void *d)
 static int dt3k_ns_to_timer(unsigned int timer_base, unsigned int *nanosec,
 			    unsigned int flags)
-	int divider, base, prescale;
+	unsigned int divider, base, prescale;
-	/* This function needs improvment */
+	/* This function needs improvement */
 	/* Don't know if divider==0 works. */
 	for (prescale = 0; prescale < 16; prescale++) {
@@ -358,7 +358,7 @@ static int dt3k_ns_to_timer(unsigned int timer_base, unsigned int *nanosec,
 			divider = (*nanosec) / base;
 		case CMDF_ROUND_UP:
-			divider = (*nanosec) / base;
+			divider = DIV_ROUND_UP(*nanosec, base);
 		if (divider < 65536) {

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