[U-Boot] [PATCH] watchdog: Implement generic watchdog_reset() version

[Stefan Roese]

On 05.04.19 15:00, Stefan Roese wrote:

<snip>

>>> +		debug("Only one watchdog device used!\n");
>>> +		return;
>>> +	}
>>> +
>>> +	/*
>>> +	 * Init watchdog: This will call the probe function of the
>>> +	 * watchdog driver, enabling the use of the device
>>> +	 */
>>> +	if (uclass_get_device(UCLASS_WDT, 0,
>>> +			      (struct udevice **)&gd->watchdog_dev)) {
>>> +		debug("Watchdog: Not found!\n");
>>> +		return;
>>> +	}
>>
>> I think you should c&p what I have done in zynq/zynqmp. It means check
>> watchdog0 alias first because this is supposed to be the first primary
>> watchdog.
>>
>> zynq/zynqmp/mb code
>>          if (uclass_get_device_by_seq(UCLASS_WDT, 0, &watchdog_dev)) {
>>                  debug("Watchdog: Not found by seq!\n");
>>                  if (uclass_get_device(UCLASS_WDT, 0, &watchdog_dev)) {
>>                          puts("Watchdog: Not found!\n");
>>                          return 0;
>>                  }
>>          }
> 
> In my (internal) first version, I had exactly this code included. I
> removed the first part, as it makes no real sense to call it at this
> stage (wdt_post_bind() for the first WDT found in the system). My
> understanding is, that wdt_post_bind() will get called for all WDT
> found in the system. My current logic here is, to only register the
> first WDT found to the global watchdog_dev in GD. To prevent that
> multiple WDT are used to service the U-Boot watchdog via WATCHDOG_RESET.
> 
> Or does the DM subsystem automatically bind the watchdog0 alias first
> in its binding sequence?
> 
> I do not have a system with multiple watchdogs here, so its not that
> easy to test this. I could simulate this though somehow...

I just did some testing on this. One solution might be, to only use
uclass_get_device_by_seq() (instead of uclass_get_device) and return
if the alias is not found. This way, all watchdog devices will get
probed (bound) and only the one referenced by the alias will get used.

This means on the other hand, that an watchdog0 alias is needed in the
DT to enable the WATCHDOG_RESET U-Boot servicing, which might be not
backward compatible.

Do you have any other thought on this?

Thanks,
Stefan