linux-kernel - Re: [PATCH] rtc: cmos: Use ACPI alarm for non-Intel x86 systems too

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Message-ID: <CAHQZ30AkayKxQkLajaY6gcFbGMWb=wu3Nqxzed5yFjLo8bX4hQ@mail.gmail.com>
Date:   Fri, 17 Nov 2023 16:43:15 -0700
From:   Raul Rangel <rrangel@...gle.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Mario Limonciello <mario.limonciello@....com>,
        Pavel Machek <pavel@....cz>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        alvin.zhuge@...il.com, renzhamin@...il.com, kelvie@...vie.ca,
        Mark Hasemeyer <markhas@...omium.org>
Subject: Re: [PATCH] rtc: cmos: Use ACPI alarm for non-Intel x86 systems too

On Fri, Nov 17, 2023 at 3:57 PM Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
>
> On 14/11/2023 18:15:02-0600, Mario Limonciello wrote:
> > On 11/14/2023 16:28, Alexandre Belloni wrote:
> > > On 14/11/2023 10:06:36+0100, Pavel Machek wrote:
> > > > On Mon 2023-11-13 23:38:19, Alexandre Belloni wrote:
> > > > > On 13/11/2023 15:36:28-0600, Mario Limonciello wrote:
> > > > > > Now that the merge window is over, can this be picked up?
> > > > > >
> > > > >
> > > > > I'd be happy to invoice AMD so they get a quick response time.
> > > >
> > > > That is a really bad joke.
> > >
> > > Why would it be a joke?
> > >
> > >  From what I get this is an issue since 2021, I don't get how this is so
> > > urgent that I get a ping less than 24h after the end of the merge
> > > window.
> >
> > It's possibly longer; but I don't have a large enough sample to say that
> > it's safe that far back.
>
> Would this help this one:
> https://bugzilla.kernel.org/show_bug.cgi?id=68331

Honestly, the HPET_EMULATE_RTC code is what drove me to switch the AMD
chromebooks over to using the ACPI timer:
https://chromium-review.googlesource.com/c/chromiumos/overlays/board-overlays/+/2355073.

Ideally if the HPET was configured with proper IRQs by the firmware,
the kernel wouldn't enable the HPET legacy emulation bit. The HPET
spec defines that when the legacy replacement option bit is set, the
HPET takes control of the RTC (#8) and timer (#2) interrupts. Why it
takes over the RTC interrupt I've never understood. The HPET is not an
RTC, so it results in software having to emulate it which results in
extra complexity. If the kernel didn't set the HPET legacy emulation
bit when the HPET declared proper IRQs, then the RTC wake interrupt
would keep working as expected. I guess there's not much benefit to
fixing this anymore, now that this ACPI timer patch has landed. If a
platform were to release new firmware to define proper HPET IRQs, the
date would bump, and it would fall into the ACPI path.

>
>
>
> --
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com