On Wed, 7 Dec 2022 at 17:55, Bjorn Andersson <andersson@xxxxxxxxxx> wrote: > > On Wed, Dec 07, 2022 at 05:00:51PM +0100, Ulf Hansson wrote: > > On Thu, 1 Dec 2022 at 23:57, Bjorn Andersson <andersson@xxxxxxxxxx> wrote: > > > > > > On Wed, Oct 05, 2022 at 02:36:58PM +0530, Akhil P Oommen wrote: > > > > > > > > > > @Ulf, Akhil has a power-domain for a piece of hardware which may be > > > voted active by multiple different subsystems (co-processors/execution > > > contexts) in the system. > > > > > > As such, during the powering down sequence we don't wait for the > > > power-domain to turn off. But in the event of an error, the recovery > > > mechanism relies on waiting for the hardware to settle in a powered off > > > state. > > > > > > The proposal here is to use the reset framework to wait for this state > > > to be reached, before continuing with the recovery mechanism in the > > > client driver. > > > > I tried to review the series (see my other replies), but I am not sure > > I fully understand the consumer part. > > > > More exactly, when and who is going to pull the reset and at what point? > > > > > > > > Given our other discussions on quirky behavior, do you have any > > > input/suggestions on this? > > > > > > > Some clients like adreno gpu driver would like to ensure that its gdsc > > > > is collapsed at hardware during a gpu reset sequence. This is because it > > > > has a votable gdsc which could be ON due to a vote from another subsystem > > > > like tz, hyp etc or due to an internal hardware signal. To allow > > > > this, gpucc driver can expose an interface to the client driver using > > > > reset framework. Using this the client driver can trigger a polling within > > > > the gdsc driver. > > > > > > @Akhil, this description is fairly generic. As we've reached the state > > > where the hardware has settled and we return to the client, what > > > prevents it from being powered up again? > > > > > > Or is it simply a question of it hitting the powered-off state, not > > > necessarily staying there? > > > > Okay, so it's indeed the GPU driver that is going to assert/de-assert > > the reset at some point. Right? > > > > That seems like a reasonable approach to me, even if it's a bit > > unclear under what conditions that could happen. > > > > Generally the disable-path of the power-domain does not check that the > power-domain is actually turned off, because the status might indicate > that the hardware is voting for the power-domain to be on. Is there a good reason why the HW needs to vote too, when the GPU driver is already in control? Or perhaps that depends on the running use case? > > As part of the recovery of the GPU after some fatal fault, the GPU > driver does something which will cause the hardware votes for the > power-domain to be let go, and then the driver does pm_runtime_put(). Okay. That "something", sounds like a device specific setting for the corresponding gdsc, right? So somehow the GPU driver needs to manage that setting, right? > > But in this case the GPU driver wants to ensure that the power-domain is > actually powered down, before it does pm_runtime_get() again. To ensure > that the hardware lost its state... I see. > > The proposal here is to use a reset to reach into the power-domain > provider and wait for the hardware to be turned off, before the GPU > driver attempts turning the power-domain on again. > > > In other words, there is no reset. This is a hack to make a normally > asynchronous pd.power_off() to be synchronous in this particular case. Alright, assuming I understood your clarifications above correctly (thanks!), I think I have got a much better picture now. Rather than abusing the reset interface, I think we should manage this through the genpd's power on/off notifiers (GENPD_NOTIFY_OFF). The GPU driver should register its corresponding device for them (dev_pm_genpd_add_notifier()). The trick however, is to make the behaviour of the power-domain for the gdsc (the genpd->power_off() callback) conditional on whether the HW is configured to vote or not. If the HW can vote, it should not poll for the state - and vice versa when the HW can't vote. Would this work? Kind regards Uffe
