From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [RFC] dynamic device power management proposal Date: Tue, 27 Mar 2007 14:05:43 +0200 Message-ID: <20070327120543.GF5161@elf.ucw.cz> References: <200703221905.l2MJ5VEU017196@olwen.urbana.css.mot.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <200703221905.l2MJ5VEU017196@olwen.urbana.css.mot.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: "Scott E. Preece" Cc: linux-pm@lists.osdl.org List-Id: linux-pm@vger.kernel.org Hi! > | > And latency may be ignorable in a laptop environment, but it absolute= ly > | > isn't in embedded devices, which users expect to operate immediately,= as > | > though they were gear-driven rather than computer-driven. > | = > | What latency are you talking about? Powering up piece of hw takes one > | milisecond or something. If your /dev/dsp takes 3 seconds to power up, > | you probably need userspace policy daemon. But that is not the case, > | hw takes few miliseconds to wake up. > = > Sure, but *some* devices take substantially longer to power up or > down. If you insist that the driver should make the power down > decision, then you lump high-latency and low-latency devices together, > even though high-latency devices might be better served by separating > the semantics. High-latency devices indeed may be served better by separating the semantics. Fortunately the high-latency (we are talking >50msec here, right?) are rare enough... Like "none" in most embedded systems... Actually only common high-latency device is harddrive (spinup/spindown), and that's already handled specially with userspace hooks. Pavel -- = (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html