From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brownell Subject: Re: [PATCH] implement pm_ops.valid for everybody Date: Fri, 23 Mar 2007 11:25:23 -0700 Message-ID: <200703231125.25180.david-b@pacbell.net> References: <200703221344.l2MDi2Q9007989@olwen.urbana.css.mot.com> <200703221416.27103.david-b@pacbell.net> <20070323131515.GA12226@atomide.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20070323131515.GA12226@atomide.com> Content-Disposition: inline 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: tony@atomide.com Cc: alexey.y.starikovskiy@intel.com, ben@simtec.co.uk, linux-arm@lists.arm.linux.org.uk, dirk.behme@de.bosch.com, pavel@ucw.cz, johannes@sipsolutions.net, nico@cam.org, linux-pm@lists.linux-foundation.org, g.liakhovetski@gmx.de List-Id: linux-pm@vger.kernel.org On Friday 23 March 2007 6:15 am, tony@atomide.com wrote: > * David Brownell [070322 17:29]: > > On Thursday 22 March 2007 12:26 pm, Tony Lindgren wrote: > > > Retention is where clocks are off for a device, but power is on. > > > In this case the device registers are maintained in hardware. > > = > > Analagous to PCI D1 or D2. > = > Hmmm, I think with PCI it's just numbering where the power > consumption decreases as the nuber increases except for D3hot > and D3cold. There are additional constraints ... as the number increases, more device state can be discarded (significant!), and there are longer latencies to return to D0 (almost noise). > > > Suspend is where clocks and power are off. In this state the > > > device registers are maintained in software. > > = > > Analagous to PCI D3, especially D3cold ... although PCI D3 > > certainly allows the Vaux "power well" to power some parts > > of the device, so that not all register values get reset. > = > Maybe actually D3hot =3D retention and D3cold =3D suspend? = > = > PCI SOCs CLOCKS POWER > D3hot retention off on > D3cold suspend off off That's why I said "especially", but there's other funkiness beyond the fact that the PCI spec leaves out "clocks" and other such implementation details. In particular, ISTR transition D3hot->D0 can optionally add some level of device reset, so it's not quite as direct a mapping as D3cold. Plus there's Vaux letting PCI devices live in two overlapping power domains. - Dave > > > Laptops mostly have suspend, while socs allow both retention > > > and suspend in many cases. > > = > > Not quite true, as noted above. There are differences in how > > things are factored, but those mechanisms exist in both x86 > > and SOC worlds. One key difference from a Linux perspective > > is probably that without ACPI in the way, a SOC design can > > make much better use of the hardware PM capabilities. > > = > > Very few non-USB drivers address "retention" modes on laptops; > > USB host controller drivers need it to handle "remote wakeup", > > which one expects to work from "standby" and suspend-to-RAM. > > (Plus potentialy suspend-to-disk, but that's uncommon.) > = > Yeah, OK. > = > Tony > =