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watchdog: dw_wdt: fix signedness bug in dw_wdt_top_in_seconds()

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On 64bit platforms, "(1 << (16 + top)) / clk_get_rate(dw_wdt.clk)" is
sign-extended to 64bit then converted to unsigned 64bit, finally divide
the clk rate. If the top is the maximum TOP i.e 15, "(1 << (16 +15))"
will be sign-extended to 0xffffffff80000000, then converted to unsigned
0xffffffff80000000, which is a huge number, thus the final result is
wrong.

We fix this issue by giving usigned value(1U in this case) at first.

Let's assume clk rate is 25MHZ,
Before the patch:
dw_wdt_top_in_seconds(15) = -864612050

After the patch:
dw_wdt_top_in_seconds(15) = 85

Signed-off-by: Jisheng Zhang <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Wim Van Sebroeck <[email protected]>
This commit is contained in:
Jisheng Zhang 2015-12-15 22:25:27 +08:00 • committed by Wim Van Sebroeck
commit 3024e0d13b
1 changed files with 1 additions and 1 deletions
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2
drivers/watchdog/dw_wdt.c
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@ -81,7 +81,7 @@ static inline int dw_wdt_top_in_seconds(unsigned top)
* There are 16 possible timeout values in 0..15 where the number of
* cycles is 2 ^ (16 + i) and the watchdog counts down.
*/
return (1 << (16 + top)) / clk_get_rate(dw_wdt.clk);
return (1U << (16 + top)) / clk_get_rate(dw_wdt.clk);
}
static int dw_wdt_get_top(void)