On 22/11/16 13:31, Ulf Hansson wrote: > On 22 November 2016 at 12:12, Jon Hunter <jonathanh@xxxxxxxxxx> wrote: >> On 16/11/16 12:53, Rafael J. Wysocki wrote: ... >>> There is a design limitation to that, however. >>> >>> The PM domain concept really is about intercepting the flow of PM >>> callbacks for a device in order to carry out additional operations, >>> not covered by the bus type or driver. That's why there is only one >>> set of PM domain callbacks per device and I don't quite see how and >>> why it would be useful to add more of them in there. >> >> Sorry for the delay. >> >> We do, however, support the nesting of power-domains to allow more than >> one power-domain to be controlled for a device. For the current >> implementations that use nested power-domains, I am not sure if the >> power-domains are truly nested or just describing a relationship between >> power-domains. >> >> Nesting power-domains could also work for the Tegra XHCI device. >> However, I don't wish to statically nest the power-domains in >> device-tree where they are defined so they are always nested, because >> this may not be always necessary. However, I would rather the client of >> the power-domains specify which power-domains they require and >> dynamically nested the power-domains at runtime. This is slightly >> different to what I proposed in this RFC, but it is not really beyond >> the bounds of what we support today IMO. What is missing is a means to >> do this dynamically and not statically. > > Hmm, going back to the original post for this thread. > > This more or less sounds very similar as the case for when Rajendra > described the problem for the video decode block in msm8996, except > that in this case you already have couple of different struct devices > available that for you could deploy runtime PM. In this case there is only one device, so ... > Then, wouldn't it be possible to assign a parent/child relationship > for these devices, each device has its own corresponding PM domain - > instead of having to dynamically nest PM domains. ... no that will not work in this case unless we create some sort of dummy parent device but I was hoping to avoid that. > Runtime PM will help to make sure parent devices are always active > when child devices also are active. > >> >> By the way, I am not sure if you are suggesting that for devices that >> may need multiple power-domains we should architect the driver >> differently and split it up in some way such that we have a power-domain >> per device. But for the case of the Tegra XHCI it is quite complex >> because the driver loads firmware which runs on a micro-controller and >> we need to manage the various power-domains that are used. > > Again, if it's possible to model the topology by using parent/child > devices, and deploy runtime PM for them, then we shouldn't need more > than one PM domain per device. I am not sure that works here though, > but just and idea. It is really not too different from how we nest power-domains today. In fact I can manually nest them and add them to the device in the driver with the existing genpd APIs. However, I don't have a meaningful way to describe the power-domains that are used by the device in DT because there is more than one. Cheers Jon -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
