CVE-2026-98946: drm/vc4: Disable the V3D interrupt across runtime suspend

In the Linux kernel, the following vulnerability has been resolved:

drm/vc4: Disable the V3D interrupt across runtime suspend

vc4irqdisable() masks the V3D interrupt sources and then calls synchronizeirq() before the V3D is powered down. However, by itself, this is not enough to quiesce the interrupt handler.

synchronizeirq() waits for handlers that have already set IRQDIRQINPROGRESS, and for irqchips reporting IRQCHIPSTATEACTIVE. A GIC interrupt chip is able to mark an interrupt active as soon as a CPU acknowledges it, so there these checks cover the whole dispatch path. On RPi 0-3, however, the interrupt controller is ARMCTRL, which has no active state. A CPU that has read the hwirq out of the pending register but has not yet reached handlelevelirq() stays invisible to synchronizeirq().

During a power transition, vc4irq() may therefore run after the power domain is off, where every V3D register read will return 0xdeadbeef. 0xdeadbeef has FLDONE, FRDONE and OUTOMEM set. This problem doesn't trigger NULL pointer dereference issues only because the functions vc4irqfinishbinjob() and vc4irqfinishrenderjob() return early when there is no job pointer, but OUTOMEM is still able to schedule vc4overflowmemwork() after vc4irqdisable() has already cancelled it.

Therefore, fix the spurious interrupts by disabling the interrupt line across the PM transition. To preserve the enable/disable balance, move vc4irqinstall() and request the IRQ line disabled before the first runtime resume.