On Wednesday, September 12, 2012, Dave Airlie wrote: > On Wed, Sep 12, 2012 at 7:32 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, 11 Sep 2012, Rafael J. Wysocki wrote: > > > >> Hi, > >> > >> On Tuesday, September 11, 2012, Dave Airlie wrote: > >> > Hi Rafael, > >> > > >> > I've been investigating runtime PM support for some use-cases on GPUs. > >> > > >> > In some laptops we have a secondary GPU (optimus) that can be powered > >> > up for certain 3D tasks and then turned off when finished with. Now I > >> > did an initial pass on supporting it without using the kernel runtime > >> > PM stuff, but Alan said I should take a look so here I am. > >> > >> Alan Stern or Alan Cox? :-) > >> > >> > While I've started to get a handle on things, we have a bit of an > >> > extra that I'm not sure we cater for. > >> > > >> > Currently we get called from the PCI layer which after we are finished > >> > with our runtime suspend callback, will go put the device into the > >> > correct state etc, however on these optimus/powerxpress laptops we > >> > have a separate ACPI or platform driver controlled power switch that > >> > we need to call once the PCI layer is finished the job. This switch > >> > effectively turns the power to the card completely off leaving it > >> > drawing no power. > >> > > >> > No we can't hit the switch from the driver callback as the PCI layer > >> > will get lost, so I'm wondering how you'd envisage we could plug this > >> > in. > >> > >> Hmm. In principle we might modify pci_pm_runtime_suspend() so that it > >> doesn't call pci_finish_runtime_suspend() if pci_dev->state_saved is > >> set. That would actually make it work in analogy with pci_pm_suspend_noirq(), > >> so perhaps it's not even too dangerous. > > > > This sounds more like a job for a power domain. Unless the power > > switch is already in the device hierarchy as a parent to the PCI > > device. > > I'll have to investigate power domains then, > > The switch is hidden in many different places, one some laptops its in > a ACPI _DSM on one GPU, on others its in an ACPI _DSM on the other > one, in some its in a different ACPI _DSM, then we have it in the ACPI > ATPX method on others, and finally Apple have it in a piece of hw that > isn't just on the LPC bus or somewhere like that. > > Currently we just hide it all inside vga_switcheroo and I'd just need > an interface to call that once the layers have stopped poking > registers in PCI config space, if we could fix PCI runtime suspend so > the driver was the last to get called then that would also not suck. Well, as I said, we may try to change the PCI layer so that it doesn't access the device any more in pci_pm_runtime_suspend() if it sees that pci_dev->state_saved has been set by the driver's callback. Then, your drivers would only need to set pci_dev->state_saved in their .runtime_suspend() callbacks. Alternatively, which may be less hackish but more work, you can set the pm_domain pointer in the device structure to a struct dev_pm_domain whose ops will just call the corresponding bus type's ops except for .runtime_suspend() that will execute the additional ACPI stuff after calling the bus type's method. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
