Re: [PATCH 4/10] watchdog: bcm63xx_wdt: Handle hardware interrupt and remove software timer

Simon Arlott
2015-11-25T20:28:59Z

On 25/11/15 20:14, Jonas Gorski wrote:
> On Tue, Nov 24, 2015 at 7:21 PM, Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org> wrote:
>> On Sun, Nov 22, 2015 at 02:05:16PM +0000, Simon Arlott wrote:
>>> There is a level triggered interrupt for the watchdog timer as part of
>>> the bcm63xx_timer device. The interrupt occurs when the hardware watchdog
>>> timer reaches 50% of the remaining time.
>>>
>>> It is not possible to mask the interrupt within the bcm63xx_timer device.
>>> To get around this limitation, handle the interrupt by restarting the
>>> watchdog with the current remaining time (which will be half the previous
>>> timeout) so that the interrupt occurs again at 1/4th, 1/8th, etc. of the
>>> original timeout value until the watchdog forces a reboot.
>>>
>>> The software timer was restarting the hardware watchdog with a 85 second
>>> timeout until the software timer expired, and then causing a panic()
>>> about 42.5 seconds later when the hardware interrupt occurred. The
>>> hardware watchdog would not reboot until a further 42.5 seconds had
>>> passed.
>>>
>>> Remove the software timer and rely on the hardware timer directly,
>>> reducing the maximum timeout from 256 seconds to 85 seconds
>>> (2^32 / WDT_HZ).
>>>
>>
>> Florian,
>>
>> can you have a look into this patch and confirm that there is no better
>> way to clear the interrupt status ?
>
> While the watchdog interrupt can't be masked, it should be able to be
> cleared by writing 1 to the appropriate bit in the timer block's
> interrupt status register. At least the broadcom sources do so.

Not according to the hardware itself:
[ 6.674626] watchdog watchdog0: warning timer fired, reboot in 7499ms
[ 6.681212] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[ 6.688583] watchdog watchdog0: warning timer fired, reboot in 7486ms
[ 6.695181] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[ 6.702554] watchdog watchdog0: warning timer fired, reboot in 7472ms
[ 6.709158] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[ 6.716529] watchdog watchdog0: warning timer fired, reboot in 7458ms
[ 6.723135] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[ 6.730538] watchdog watchdog0: warning timer fired, reboot in 7444ms
[ 6.737121] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[ 6.744482] watchdog watchdog0: warning timer fired, reboot in 7430ms
[ 6.751090] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08

typedef struct Timer {
uint16 unused0;
byte TimerMask;
#define TIMER0EN 0x01
#define TIMER1EN 0x02
#define TIMER2EN 0x04
byte TimerInts;
#define TIMER0 0x01
#define TIMER1 0x02
#define TIMER2 0x04
#define WATCHDOG 0x08
...