soc: apple: apple-pmgr-pwrstate: Mark on-at-boot PDs as DEFER_OFF

We consider any domains that are found to be powered on at boot as
potentially critical for probing consumer devices. This prevents
badness like the boot-time display controller being powered down as soon
as its IOMMU probes.

Fixes a pile of PD probe order dependencies and races that have required
ALWAYS_ON workaround hacks until now, including:

- ANS2 (NVMe) breaking if left on at handoff.
- DISP0/DCP (boot display) completely breaking.
- PM domains failing to probe when their parent was inadvertently shut
  down before the child probed.
- PCIe losing state/fuse info/etc when it powers down before the driver
  is ready.
- Touch Bar (DFR) display controller losing bootloader-configured state
  before its driver can probe and save it.

The downside is that any spuriously on domains will remain on if their
drivers are missing. We consider missing drivers that never get loaded a
downstream bug. For older kernels running on newer DTs with extra
devices, this shouldn't cause any major problems other than perhaps
slightly increased power consumption (and we can always fix it in the
bootloader by powering down those PDs if they don't need to be left on,
since the bootloader is updated together with the DTs).

Signed-off-by: Hector Martin <marcan@marcan.st>

Author: marcan

drivers/pmdomain/apple/pmgr-pwrstate.c

@@ -242,6 +242,8 @@ static int apple_pmgr_ps_probe(struct platform_device *pdev)
 			/* Turn it on so pm_genpd_init does not fail */
 			active = apple_pmgr_ps_power_on(&ps->genpd) == 0;
 		}
+	} else if (active) {
+		ps->genpd.flags |= GENPD_FLAG_DEFER_OFF;
 	}
 
 	/* Turn on auto-PM if the domain is already on */