linux-kernel - Re: [PATCH 5/5] intel_idle: Add S0ix validation

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Message-ID: <20160602205338.4a16760a@lxorguk.ukuu.org.uk>
Date:	Thu, 2 Jun 2016 20:53:38 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	"dbasehore ." <dbasehore@...omium.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux-pm mailing list <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/5] intel_idle: Add S0ix validation

> How would this spuriously trigger during boot? This code is only run
> during freeze. If there's some issue with not entering S0ix before a
> module or firmware is loaded, it's better to not use suspend to idle
> until those are in place.

Ok yes you are correct it's not likely to trigger during boot (although
if you close the lid during boot...)

> I'm not familiar with the ISH driver. How does it prevent entry into
> S0ix? I would argue that you don't want to use suspend to idle on a
> Skylake system that can't enter S0ix and instead use suspend to RAM.

Several IP blocks on the systems do their own power management if present
and enabled by the firmware. If they do not have drivers loaded then you
will not be able to enter some power states. Thus you'll now get warnings
if you try to freeze such a system and those warnings are not themselves
terribly helpful to a user.

It's a good debug feature, but it doesn't belong anywhere but debug menus
and off by default. If you want to ship it enabled in ChromeOS for
product fine, but I don't think it belongs on for everywhere and
everything.

Alan