watchdog: bcm2835: Clamp timeouts to the h/w max#7432
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The kernel watchdog framework permits arbitrarily large timeout values to be requested; if the request exceeds the maximum interval supported by the hardware, the kernel's watchdogd thread automatically pings the hardware to keep it alive until the time remaining until the expected reset fits within the hardware's registers. Although each watchdog driver reports the largest timeout, the onus is on them to limit the value passed in: Drivers implementing max_hw_heartbeat_ms set the hardware watchdog heartbeat to the minimum of timeout and max_hw_heartbeat_ms. bcm2835_wdt instead masks off the high bits of the counter, meaning that the actual time until the device resets is (requested_time % 16). This was spotted when the requested timeout was 1 minute, giving an actual timeout of 12 seconds, but a requested 100 seconds becomes 4 seconds. Correct bcm2835_wdt_start to implement the expected behaviour. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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Jun 11, 2026
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The kernel watchdog framework permits arbitrarily large timeout values to be requested; if the request exceeds the maximum interval supported by the hardware, the kernel's watchdogd thread automatically pings the hardware to keep it alive until the time remaining until the expected reset fits within the hardware's registers. Although each watchdog driver reports the largest timeout, the onus is on them to limit the value passed in:
Drivers implementing max_hw_heartbeat_ms set the hardware watchdog
heartbeat to the minimum of timeout and max_hw_heartbeat_ms.
bcm2835_wdt instead masks off the high bits of the counter, meaning that the actual time until the device resets is (requested_time % 16). This was spotted when the requested timeout was 1 minute, giving an actual timeout of 12 seconds, but a requested 100 seconds becomes 4 seconds.
Correct bcm2835_wdt_start to implement the expected behaviour.