On 13.01.2021 23:01, Russell King - ARM Linux admin wrote: > On Wed, Jan 13, 2021 at 10:34:53PM +0100, Heiner Kallweit wrote: >> On 13.01.2021 13:36, claudiu.bez...@microchip.com wrote: >>> On 13.01.2021 13:09, Heiner Kallweit wrote: >>>> On 13.01.2021 10:29, claudiu.bez...@microchip.com wrote: >>>>> It could enter in this mode based on request for standby or >>>>> suspend-to-mem: >>>>> echo mem > /sys/power/state >>>>> echo standby > /sys/power/state > > This is a standard way to enter S2R - I've used it many times in the > past on platforms that support it. > >> I'm not a Linux PM expert, to me it seems your use case is somewhere in the >> middle between s2r and hibernation. I *think* the assumption with s2r is >> that one component shouldn't simply cut the power to another component, >> and the kernel has no idea about it. > > When entering S2R, power can (and probably will) be cut to all system > components, certainly all components that do not support wakeup. If > the system doesn't support WoL, then that will include the ethernet > PHY. > I'm with you if we talk about a driver's suspend callback cutting power to the component it controls, or at least putting it to a power-saving state. However a driver shouldn't have to expect that during S2R somebody else cuts the power. If this would be the case, then I think we wouldn't need separate resume and restore pm callbacks in general.
> When resuming, the responsibility is of the kernel and each driver's > .resume function to ensure that the hardware state is restored. Only > each device driver that knows the device itself can restore the state > of that device. In the case of an ethernet PHY, that is phylib and > its associated PHY driver. > Also in phylib we have separate functions mdio_bus_phy_resume() and mdio_bus_phy_restore(), with the first one not fully reconfiguring the PHY. > One has to be a tad careful with phylib and PHYs compared to their > MAC devices in terms of the resume order - it has not been unheard > of over the years for a MAC device to be resumed before its connected > PHY has been. > Right.
