Re: [PATCH 7/7] hw/watchdog/wdt_aspeed: Reduce timer precision to micro-second

[Philippe Mathieu-Daudé]

On 6/22/20 2:21 AM, Andrew Jeffery wrote:
> On Wed, 17 Jun 2020, at 13:11, Philippe Mathieu-Daudé wrote:
>> Hi Andrew,
>>
>> On 6/17/20 3:18 AM, Andrew Jeffery wrote:
>>> On Tue, 16 Jun 2020, at 17:21, Philippe Mathieu-Daudé wrote:
>>>> The current implementation uses nano-second precision, while
>>>> the watchdog can not be more precise than a micro-second.
>>>
>>> What's the basis for this assertion? It's true for the AST2500 and AST2600, 
>>> but 
>>> the AST2400 can run the watchdog from either a 1MHz clock source or the APB 
>>> clock (which must be at least 16.5MHz on palmetto). The reset state on the
>>> AST2400 configures the watchdog for the APB clock rate.
>>>
>>> The Linux driver will eventually configure the watchdog for 1MHz mode
>>> regardless so perhaps the AST2400 reset state is a bit of a corner case, but
>>> I feel the assertion should be watered down a bit?
>>
>> What about this description?
>>
>> "The current implementation uses nano-second precision, but
>>  is not more precise than micro-second precision.
>>  Simplify by using a micro-second based timer.
>>  Rename the timer 'timer_us' to have the unit explicit."
> 
> So is this a limitation of QEMUTimer? I was establishing that the hardware 
> can 
> operate at greater than 1 micro-second precision.

No, I misread your comment about the AST2400 timer which can run
at more than 1Mhz.

The QEMUTimer doesn't have a such limitation; this patch
aimed to simplify the code for reviewers, but you proved
it incorrect, so let's disregard it.

Thanks for your careful review!

> 
> Andrew
>