Jon recently reported that one of the Tegra systems (Jetson TX2, aka tegra186) stopped booting with the introduction of the "IPI as IRQs" series. After a few weeks of head scratching and complete puzzlement, I obtained a board and started looking at what was happening. The interrupt hierarchy looks like this: [DEVICE] -A-> [PMC] -B-> [GIC] which seems simple enough. However, not all the devices attached to the PMC follow this hierarchy, and in some cases, the 'B' link isn't present in the HW. In other cases, neither 'A' nor 'B' are present. And yet the PMC driver creates such linkages using random hwirq values for the non-existent links, potentially overriding existing mappings in the process. "What could possibly go wrong?" It turns out that for the 'B' link, the PMC driver uses hwirq 0, which is SGI0 for the GIC, and used as the rescheduling IPI. Obviously, this doesn't go very well, nor very far, as the IPI gets routed to random drivers. Also, as the handling flow has been overridden, this interrupt never gets deactivated and can't fire anymore. Yes, this is bad. The 'A' link is less problematic, but the hwirq value is still out of the irqdomain range, and gets remapped every time a new 'A'-less driver comes up. Instead, let's trim the unused hierarchy levels as needed. This requires some checks in the upper levels of the hierarchy as we now have optional levels, but this looks a lot saner than what we currently have. With this, tegra186 is back booting on -next. I haven't tested any wake-up stuff, nor any other nvidia system (this is the only one I have). If people agree to these changes, I can take them via the irqchip tree so that they make it into the next merge window. M. Marc Zyngier (3): gpio: tegra186: Allow optional irq parent callbacks soc/tegra: pmc: Allow optional irq parent callbacks soc/tegra: pmc: Don't create fake interrupt hierarchy levels drivers/gpio/gpio-tegra186.c | 15 +++- drivers/soc/tegra/pmc.c | 142 ++++++++++++++++++++--------------- 2 files changed, 95 insertions(+), 62 deletions(-) -- 2.28.0
