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From:   "Anand K. Mistry" <amistry@google.com>
Date:   Thu, 4 Feb 2021 17:13:56 +1100
Message-ID: <CAATStaMRHai=jWr4x1cZVs2MrME+1QSqoXD75xAOQfxb723hQQ@mail.gmail.com>
Subject: Re: [PATCH] x86: Add a prompt for HPET_EMULATE_RTC
To:     Randy Dunlap <rdunlap@infradead.org>
Cc:     x86@kernel.org, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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> 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.

> 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.

-- 
Anand K. Mistry
Software Engineer
Google Australia