linux-kernel - Re: [PATCH] x86: Add a prompt for HPET_EMULATE

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Message-ID: <507e5062-f575-e034-d6fa-f1dca4bbbcc9@infradead.org>
Date:   Wed, 3 Feb 2021 22:29:55 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     "Anand K. Mistry" <amistry@...gle.com>
Cc:     x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Add a prompt for HPET_EMULATE_RTC

On 2/3/21 10:13 PM, Anand K. Mistry wrote:
>> Hi,
>>
>> When you run "make olddefconfig", should this "depends on"
>> line evaluate to true or false?
> 
> True. RTC_DRV_CMOS=y by default on x86 systems and HPET_TIMER also
> appears to default yes (on x86-64 if I'm reading this right).
> 
> Oddly, the RTC config option doesn't appear to exist. Probably a separate issue.

Yes, just a separate simple patch.

>> I.e., what are the settings of these symbols in the old .config file?
>>
>>
>>         depends on HPET_TIMER && (RTC=y || RTC=m || RTC_DRV_CMOS=m || RTC_DRV_CMOS=y)
> 
> Actually, none of these options are set in the old config.
> RTC_DRV_CMOS and HPET_TIMER appear to default to yes.
> 
>  % grep HPET .config
> CONFIG_HPET=y
> # CONFIG_HPET_EMULATE_RTC is not set
> # CONFIG_HPET_MMAP is not set
>  % grep RTC .config
> CONFIG_RTC_CLASS=y
> # CONFIG_HPET_EMULATE_RTC is not set
> CONFIG_PM_TRACE_RTC=y
> # CONFIG_RTC_HCTOSYS is not set
> 
>>
>> If not, is there some out-of-tree driver involved?
> 
> No out of tree drivers involved. I tried this on a vanilla 5.11-rc6.
> 
>> I'm having a little trouble seeing why this is needed.
> 
> So am I. But this is the magic that lets me keep
> CONFIG_HPET_EMULATE_RTC from the old config. I did manage to trace
> where the option is being overridden in the conf tool, but the
> reasoning why is beyond my knowledge.

Can you post the .config that you are feeding to 'make olddefconfig', please.
I'll take a look (or the x86 guys can do so).


thanks.
-- 
~Randy