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Re: [RFC PATCH-for-6.1 v2 6/6] hw/mips/loongson3_virt: Raise CPU clock t

From: Philippe Mathieu-Daudé
Subject: Re: [RFC PATCH-for-6.1 v2 6/6] hw/mips/loongson3_virt: Raise CPU clock to 2 GHz
Date: Sat, 10 Apr 2021 16:05:51 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1

Hi Huacai,

On 4/10/21 4:43 AM, Huacai Chen wrote:
> Hi, Philippe,
> On Fri, Apr 9, 2021 at 5:36 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>> Commit cd3a53b727d ("clock: Add clock_ns_to_ticks() function")
>> removed the limitation of using clock with a frequency of 1 GHz
>> or more.
>> The previous commit converted the MIPS CP0 timer to use this
>> new clock_ns_to_ticks() function. We can now use a clock of
>> 2 GHz with the Loongson3 virt board.
> Yes, we can do this, but why should we do this? I don't think this can
> bring any advantages.

IIRC this was how you sent the earlier series, then we had to reduce
the frequency to <1GHz due to the DIV#0 bug. Now it is fixed I thought
you'd get this back.

I spent time with the R4K timer because it is often used by embedded
firmwares, and a mismatch with the CPU clock makes firmware not work
well. I suppose when using Linux guests it is not a real issue, because
1/ if there is another timer (different peripheral on a system-on-soc)
Linux will use it first, 2/ Linux does some early check to adapt with
the tick rate IIRC (it doesn't assume a precise rate).

I'm fine with the current Loongson3 virt board behavior with TCG,
so let's disregard this patch.



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