Am Dienstag, 7. August 2018, 10:54:05 CEST schrieb Marc Zyngier:

pm_runtime_get_if_in_use can fail: either PM has been disabled
altogether (-EINVAL), or the device hasn't been enabled yet (0).
Sadly, the Rockchip IOMMU driver tends to conflate the two things
by considering a non-zero return value as successful.

This has the consequence of hiding other bugs, so let's handle this
case throughout the driver, with a WARN_ON_ONCE so that we can try
and work out what happened.

Fixes: 0f181d3cf7d98 ("iommu/rockchip: Add runtime PM support")
Signed-off-by: Marc Zyngier <redacted>

With Rockchip platforms always selecting PM
[see other longer thread in reply to the patch]

Reviewed-by: Heiko Stuebner <heiko@sntech.de>