linux-kernel - Re: [PATCH/RFC v2 02/12] PM / Domains: Add DT bindings for PM QoS device latencies

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Message-ID: <7heguzbd4z.fsf@deeprootsystems.com>
Date:	Thu, 25 Sep 2014 14:31:40 -0700
From:	Kevin Hilman <khilman@...nel.org>
To:	Geert Uytterhoeven <geert+renesas@...der.be>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Philipp Zabel <philipp.zabel@...il.com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC v2 02/12] PM / Domains: Add DT bindings for PM QoS device latencies

Geert Uytterhoeven <geert+renesas@...der.be> writes:

> PM QoS device start/stop and save/restore state latencies are more or
> less properties of the hardware.
> In legacy code, they're specified from platform code.
> On DT platforms, their values should come from DT.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Should these properties be called "linux,*-latency"?

Hmm, the start/stop latencies are clearly properties of the hardware,
but the save/restore latencies seem to be a function of the driver.
e.g., some drivers may keep a shadow copy of their registers in memory
so the save time is minimized.

I don't have too strong of an opinion on this, but probably the drivers
should just add their own values to the start/stop latencies to add the
linux specific overhead.

Kevin
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