7dc16b8484
explain the subtle side effects that are going to happen and why we go ahead and ack the interrupt source. This stuff is tricky to get right. Also, emperical tests have shown that doing a shutdown in attach to be ineffectual, so remove it from there. Analysis of the code paths shows that nearly identical writes to these registers happen in later parts of the code. The hanging problem on thinkpads when we change the interrupt routing type is something else.