Hello, On Sun Nov 26, 2023 at 11:36 PM CET, Kevin Hilman wrote: > Théo Lebrun <theo.lebrun@xxxxxxxxxxx> writes: > > On Wed Nov 22, 2023 at 11:23 PM CET, Kevin Hilman wrote: > >> Théo Lebrun <theo.lebrun@xxxxxxxxxxx> writes: > >> The point is to signal to the power domain the device is in that it can > >> power on/off. These IP blocks are (re)used on many different SoCs, so > >> the driver should not make any assumptions about what power domain it is > >> in (if any.) > > > > On my platform, when the device is attached to the PD it gets turned on. > > That feels logical to me: if a driver is not RPM aware it "just works". > > It "just works"... until the domain gets turned off. > > > Are there platforms where RPM must get enabled for the attached > > power-domains to be turned on? > > Yes, but but more importantly, there are platforms where RPM must get > enabled for the power domain to *stay* on. For example, the power > domain might get turned on due to devices probing etc, but as soon as > all the RPM-enabled drivers drop their refcount, the domain will turn > off. If there is a device in that domain with a non-RPM enabled driver, > that device will be powered off anc cause a crash. OK, that makes sense, thanks for taking the time to explain. This topic makes me see two things that I feel are close to being bugs. I'd be curious to get your view on both. - If a device does not use RPM but its children do, it might get its associated power-domain turned off. That forces every single driver that want to stay alive to enable & increment RPM. What I naively expect: a genpd with a device attached to it that is not using RPM should mean that it should not be powered off at runtime_suspend. Benefit: no RPM calls in drivers that do not use it, and the behavior is that the genpd associated stays alive "as expected". - If a device uses RPM & has a refcount strictly positive, its associated power-domain gets turned off either way at suspend_noirq. That feels non-intuitive as well. What I naively expect: check for RPM refcounts of attached devices when doing suspend_noirq of power-domains. Benefit: control of what power-domains do from attached devices is done through the RPM API. Regards, -- Théo Lebrun, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
