watchdog: dw_wdt: fix signedness bug in dw_wdt_top_in_seconds()
authorJisheng Zhang <jszhang@marvell.com>
Tue, 15 Dec 2015 14:25:27 +0000 (22:25 +0800)
committerWim Van Sebroeck <wim@iguana.be>
Sun, 27 Dec 2015 20:04:50 +0000 (21:04 +0100)
commit3024e0d13b0f34536f94bf0d7cc11443beeee9c5
treeac821866889cf44a9e06917322331995c9af775b
parent5889f06bd31d542766046faa6b17d957c08e1484
watchdog: dw_wdt: fix signedness bug in dw_wdt_top_in_seconds()

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 <jszhang@marvell.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
drivers/watchdog/dw_wdt.c