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! 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
