On 23 May 2018 at 11:45, Jon Hunter <jonathanh@xxxxxxxxxx> wrote: > > On 23/05/18 10:33, Ulf Hansson wrote: >> >> On 23 May 2018 at 11:27, Rajendra Nayak <rnayak@xxxxxxxxxxxxxx> wrote: >>> >>> >>> >>> On 05/23/2018 02:37 PM, Jon Hunter wrote: >>>> >>>> >>>> On 23/05/18 07:12, Ulf Hansson wrote: >>>> >>>> ... >>>> >>>>>>>>> Thanks for sending this. Believe it or not this has still been on >>>>>>>>> my to-do list >>>>>>>>> and so we definitely need a solution for Tegra. >>>>>>>>> >>>>>>>>> Looking at the above it appears that additional power-domains >>>>>>>>> exposed as devices >>>>>>>>> to the client device. So I assume that this means that the drivers >>>>>>>>> for devices >>>>>>>>> with multiple power-domains will need to call RPM APIs for each of >>>>>>>>> these >>>>>>>>> additional power-domains. Is that correct? >>>>>>>> >>>>>>>> >>>>>>>> They can, but should not! >>>>>>>> >>>>>>>> Instead, the driver shall use device_link_add() and >>>>>>>> device_link_del(), >>>>>>>> dynamically, depending on what PM domain that their original device >>>>>>>> needs for the current running use case. >>>>>>>> >>>>>>>> In that way, they keep existing runtime PM deployment, operating on >>>>>>>> its original device. >>>>>>> >>>>>>> >>>>>>> OK, sounds good. Any reason why the linking cannot be handled by the >>>>>>> above API? Is there a use-case where you would not want it linked? >>>>>> >>>>>> >>>>>> I am guessing the linking is what would give the driver the ability to >>>>>> decide which subset of powerdomains it actually wants to control >>>>>> at any point using runtime PM. If we have cases wherein the driver >>>>>> would want to turn on/off _all_ its associated powerdomains _always_ >>>>>> then a default linking of all would help. >>>>> >>>>> >>>>> First, I think we need to decide on *where* the linking should be >>>>> done, not at both places, as that would just mess up synchronization >>>>> of who is responsible for calling the device_link_del() at detach. >>>>> >>>>> Second, It would in principle be fine to call device_link_add() and >>>>> device_link_del() as a part of the attach/detach APIs. However, there >>>>> is a downside to such solution, which would be that the driver then >>>>> needs call the detach API, just to do device_link_del(). Of course >>>>> then it would also needs to call the attach API later if/when needed. >>>>> Doing this adds unnecessary overhead - comparing to just let the >>>>> driver call device_link_add|del() when needed. On the upside, yes, it >>>>> would put less burden on the drivers as it then only needs to care >>>>> about using one set of functions. >>>>> >>>>> Which solution do you prefer? >>>> >>>> >>>> Any reason why we could not add a 'boolean' argument to the API to >>>> indicate whether the new device should be linked? I think that I prefer the >>>> API handles it, but I can see there could be instances where drivers may >>>> wish to handle it themselves. >>>> >>>> Rajendra, do you have a use-case right now where the driver would want >>>> to handle the linking? >>> >>> >>> So if I understand this right, any driver which does want to control >>> individual powerdomain state would >>> need to do the linking itself right? >>> >>> What I am saying is, if I have device A, with powerdomains X and Y, and >>> if I want to turn on only X, >>> then I would want only X to be linked with A, and at a later point if I >>> want both X and Y to be turned on, >>> I would then go ahead and link both X and Y to A? Is that correct or did >>> I get it all wrong? >> >> >> Correct! >> >>> >>> I know atleast Camera on msm8996 would need to do this since it has 2 vfe >>> powerdoamins, which can be >>> turned on one at a time (depending on what resolution needs to be >>> supported) or both together if we >>> really need very high resolution using both vfe modules. >> >> >> I think this is also the case for the Tegra XUSB subsystem. >> >> The usb device is always attached to one PM domain, but depending on >> if super-speed mode is used, another PM domain for that logic needs to >> be powered on as well. >> >> Jon, please correct me if I am wrong! > > > Yes this is technically correct, however, in reality I think we are always > going to enable the superspeed domain if either the host or device domain is > enabled. So we would probably always link the superspeed with the host and > device devices. Why? Wouldn't that waste power if the superspeed mode isn't used? Kind regards Uffe -- 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
