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Re: [PATCH 7/7] hw/watchdog/wdt_aspeed: Reduce timer precision to micro-
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH 7/7] hw/watchdog/wdt_aspeed: Reduce timer precision to micro-second |
Date: |
Mon, 22 Jun 2020 10:43:52 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 |
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
>
- [PATCH 2/7] block/qcow2: Document cache_clean_interval field holds seconds, (continued)
- [PATCH 2/7] block/qcow2: Document cache_clean_interval field holds seconds, Philippe Mathieu-Daudé, 2020/06/16
- [PATCH 3/7] block/curl: Reduce timer precision to milli-second, Philippe Mathieu-Daudé, 2020/06/16
- [PATCH 4/7] hw/virtio/virtio-balloon: Rename timer field including 'ms' unit, Philippe Mathieu-Daudé, 2020/06/16
- [PATCH 5/7] hw/rtc/m48t59: Reduce timer precision to milli-second, Philippe Mathieu-Daudé, 2020/06/16
- [PATCH 6/7] hw/ipmi/ipmi_bmc_extern: Reduce timer precision to milli-second, Philippe Mathieu-Daudé, 2020/06/16
- [PATCH 7/7] hw/watchdog/wdt_aspeed: Reduce timer precision to micro-second, Philippe Mathieu-Daudé, 2020/06/16
Re: [PATCH 0/7] misc: Reduce QEMUTimer pressure by using lower precision when possible, Paolo Bonzini, 2020/06/18