On Wed, 22 Jul 2015, Sylvain Munaut wrote: > Hi Alan, > > > Thanks for the details. > > > >> tl;dr : Should device allowed to do runtime pm that have no driver go > >> to D3 on their own ? > > > > Quick answer: See the comments at the start of local_pci_probe() in > > drivers/pci/pci-driver.c. PCI devices without a kernel driver are > > always left in D0, regardless of the runtime PM status. This is > > because userspace may try to use the device, and the kernel wouldn't > > know to take the device out of D3 when that happens. > > Does linux expose some way for userspace to transition the device to > another power state without the need for a driver ? I don't think so. Of course, such a thing could be added. One simple way to do it would be to create a "do-nothing" driver that would allow userspace to access the device directly and would include runtime PM suport. > I looked at the docs and tried poking some of the sysfs files, but > except enabling/disabling the runtme pm, I couldn't really change > anything, but maybe I missed something. You probably didn't miss anything. > >> And should pci root bridge go to D3 when all the > >> device on them are on D3 ? > > > > I don't know the answer to that. It's probably closely related to the > > issue of whether PCI bridges need to have a kernel driver. > > OK. > > Do you know if there could be any adverse effect of transitioning it myself ? > > Basically I'm doing this when turning off the card : > > struct pci_dev *port_dev = pci_upstream_bridge(pdev); > > pci_save_state(port_dev); > pci_clear_master(port_dev); > pci_disable_device(port_dev); > pci_set_power_state(port_dev, PCI_D3hot); > > > And this when waking it up : > > pci_set_power_state(port_dev, PCI_D0); > pci_restore_state(port_dev); > pci_enable_device(port_dev); > pci_set_master(port_dev); > > (I removed the return value checking to make the code more concise here). That seems reasonable. But I am far from an expert on PCI or Linux's PCI subsystem. You really should address this sort of question to the linux-pci mailing list. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
