watchdog: meson: Fix the wrong value of left time

[ Upstream commit 2c77734642d52448aca673e889b39f981110828b ]

The left time value is wrong when we get it by sysfs. The left time value
should be equal to preset timeout value minus elapsed time value. According
to the Meson-GXB/GXL datasheets which can be found at [0], the timeout value
is saved to BIT[0-15] of the WATCHDOG_TCNT, and elapsed time value is saved
to BIT[16-31] of the WATCHDOG_TCNT.

[0]: http://linux-meson.com

Fixes: 683fa50f ("watchdog: Add Meson GXBB Watchdog Driver")
Signed-off-by: NXingyu Chen <xingyu.chen@amlogic.com>
Acked-by: NNeil Armstrong <narmstrong@baylibre.com>
Reviewed-by: NKevin Hilman <khilman@baylibre.com>
Reviewed-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NWim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>

drivers/watchdog/meson_gxbb_wdt.c

@@ -89,8 +89,8 @@ static unsigned int meson_gxbb_wdt_get_timeleft(struct watchdog_device *wdt_dev)
 
 	reg = readl(data->reg_base + GXBB_WDT_TCNT_REG);
 
-	return ((reg >> GXBB_WDT_TCNT_CNT_SHIFT) -
-		(reg & GXBB_WDT_TCNT_SETUP_MASK)) / 1000;
+	return ((reg & GXBB_WDT_TCNT_SETUP_MASK) -
+		(reg >> GXBB_WDT_TCNT_CNT_SHIFT)) / 1000;
 }
 
 static const struct watchdog_ops meson_gxbb_wdt_ops = {