> On 23. 8. 2022, at 13:31, Mark Brown <broonie@xxxxxxxxxx> wrote: > > On Tue, Aug 23, 2022 at 09:33:36AM +0200, Martin Povišer wrote: >>> On 22. 8. 2022, at 19:39, Mark Brown <broonie@xxxxxxxxxx> wrote: >>> On Fri, Aug 19, 2022 at 02:54:29PM +0200, Martin Povišer wrote: >>>> + /* >>>> + * We can't power up the device earlier than this because >>>> + * the power state driver would error out on seeing the device >>>> + * as clock-gated. >>>> + */ >>>> + cl->pd_link = device_link_add(mca->dev, cl->pd_dev, >>>> + DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | >>>> + DL_FLAG_RPM_ACTIVE); > >>> I'm not clear on this dynamically adding and removing device links stuff >>> - it looks like the main (only?) purpose is to take a runtime PM >>> reference to the target device which is fine but it's not clear why >>> device links are involved given that the links are created and destroyed >>> every time the DAI is used, AFAICT always in the same fixed >>> relationship. It's not a problem, it's just unclear. > >> Indeed the only purpose is powering up the cluster’s power domain (there’s >> one domain for each cluster). Adding the links is the only way I know to >> do it. They need to be added dynamically (as opposed to statically linking, >> say, the DAI’s ->dev to the cluster’s ->pd_dev, which I guess may do >> something similar), because we need to sequence the power-up/power-down >> with the enablement of the clocks. > > You could also just do the underlying runtime power management > operations directly couldn't you? It's not clear what the device link > stuff is adding. This seems to be the way to do it. Quoting from documentation of dev_pm_domain_attach_by_id, by which we obtain the mca->dev and cl->pd_dev the link is between: * This function should typically be invoked by a driver during the probe phase, * in case its device requires power management through multiple PM domains. The * driver may benefit from using the received device, to configure device-links * towards its original device. Depending on the use-case and if needed, the * links may be dynamically changed by the driver, which allows it to control * the power to the PM domains independently from each other. -- Martin
