[PATCH] i915: Remove IMR masking during interrupt handler, and restart it if needed.

The IMR masking was a technique recommended for avoiding getting stuck with no interrupts generated again in MSI mode. It kept new IIR bits from getting set between the IIR read and the IIR write, which would have otherwise prevented an MSI from ever getting generated again. However, this caused

[PATCH] i915: Remove IMR masking during interrupt handler, and restart it if needed.

The IMR masking was a technique recommended for avoiding getting stuck with no interrupts generated again in MSI mode. It kept new IIR bits from getting set between the IIR read and the IIR write, which would have otherwise prevented an MSI from ever getting generated again. However, this caused