linux-kernel - Re: [RFC PATCH v4 8/8] acpi_idle: Disallow play

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Message-ID: <Z0SU+cv9UyXfQdS1@BLRRASHENOY1.amd.com>
Date: Mon, 25 Nov 2024 20:47:13 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	rafael.j.wysocki@...el.com, len.brown@...el.com,
	artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com,
	tglx@...utronix.de
Subject: Re: [RFC PATCH v4 8/8] acpi_idle: Disallow play_dead with FFH cstate
 on AMD platforms

On Mon, Nov 25, 2024 at 03:56:25PM +0100, Patryk Wlazlyn wrote:
> > So I don't like this. Less exceptions is better.
> >
> > This *SHOULD* never trigger on AMD anyway, because they recommend IO
> > port C[23]. But if their partner BIOS engineer does a wobbly and they
> > end up in MWAIT anyway, it *should* all work regardless.
> Agreed.
> I thought relaying on BIOS to not put FFH states there was a concern.
> I believe Gautham confirmed that AMD would be fine executing that,
> it's just that they prefer ioidle (or hlt?).

Yes, HLT or IOPORT based idle states for CPU Offline are
preferrable. But FFH based idle states work just fine.

--
Thanks and Regards
gautham.