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. 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(). 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... 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. Regards, Bjorn
