x86/ioapic: Check attr against the previous setting when programmed more than once

When programming ioapic pinX more than once, current code
does not check whether the later attr (trigger & polarity) is the
same as the former or not.

This causes broken semantics which can be observed in a qemu q35
machine, where ioapic's ioredtbl[x] can never be set as low-active,
even if the hpet driver registered it.

And hpet driver may share a high-level active IRQ line with other
devices. So in qemu, when hpet-dev asserts low-level as kernel
expects, the kernel has no response.

With this patch, we can observe an ioredtbl[x] set as low-active
for hpet.

Fix it by reporting -EBUSY to the caller, when attr is different.

Signed-off-by: Liu Ping Fan <[email protected]>
Cc: Kevin Hao <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Yinghai Lu <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
[ Made small readability edits to both the changelog and the code. ]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions