Re: [PATCH] watchdog: sbsa: Support architecture version 1

[Guenter Roeck <linux@roeck-us.net>]

On 5/10/21 7:49 PM, Shaokun Zhang wrote:
> Hi Guenter,
> 
> On 2021/5/10 21:16, Guenter Roeck wrote:
>> On 5/10/21 1:25 AM, Shaokun Zhang wrote:
>>> Hi Guenter,
>>>
>>> On 2021/5/10 12:25, Guenter Roeck wrote:
>>>> On 5/9/21 8:41 PM, Shaokun Zhang wrote:
>>>>> Arm Base System Architecture 1.0[1] has introduced watchdog
>>>>> revision 1 that increases the length the watchdog offset
>>>>
>>>> Is that how they call the watchdog count register ?
>>>>
>>>
>>> I think yes.
>>>
>>>> Also, doesn't that mean that the maximum timeout supported
>>>> by the hardware is now larger ?
>>>
>>> No, maximum timeout is the same. But the clock can be higher than
>>> before. For Armv8.6, The frequency of CNTFRQ_EL0 is standardized to
>>> a frequency of 1GHz which will set gwdt->clk. If the timeout is
>>> greater than 4(second), the 32-bit counter(WOR) is not enough.
>>>
>>
>> The maximuma timeout is limited with
>>
>> wdd->max_hw_heartbeat_ms = U32_MAX / gwdt->clk * 1000;
>>> You did not update that calculation. That means that the maximuma
>> timeout is still U32_MAX / gwdt->clk * 1000, which still fits
>> into 32 bit.
> 
> Correct, I will fix this in next version.
> 
>>
>> Please correct me if I am missing something.
>>
> 
> My bad, you are right. The maximum timeout shall be
> 0xFFFF.FFFF.FFFF / 1000.000.000(1GHz) which is larger than before
> 0xFFFF.FFFF / 100.000.000(100MHz) by the hardware.
> 
> Can I do like this, after the version is got and check the version?
>          sbsa_gwdt_set_timeout(wdd, wdd->timeout);
> +       sbsa_gwdt_get_version(wdd);
> +       if (wdd->version > 0)
> +               wdd->max_hw_heartbeat_ms = GENMASK_ULL(47, 0) / gwdt->clk * 1000;
> 

I would suggest to set max_hw_heartbeat_ms in one place
to avoid confusion. Either check the version earlier,
or move setting both max_hw_heartbeat_ms values
after the call to sbsa_gwdt_get_version().

Thanks,
Guenter