On Friday 23 March 2007 6:15 am, tony@xxxxxxxxxxx wrote: > * David Brownell <david-b@xxxxxxxxxxx> [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 = retention and D3cold = 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 > _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
