1) because the CS5536 is not associated with a x86 CPU, interrupts are not
ack'ed as it expects so interrupts cannot configured as edge-triggered
(as is expected for a PCIIDE in compat mode)
2) the PATA->SATA bridge ignores the WDC_IDS (interrupt disable bit) so
the PATA IRQ line gets asserted when resetting or running some polled
commands. It also wrongly asserts IRQ when the (nonexistent) slave
device is selected
2) wouldn't be an issue with edge-triggered interrupt because we would
get a spurious interrupt and continue operation, a new interrupt only shows
up when the PATA IRQ line goes low and high again. But because of 1),
we get an unclearable interrupt instead, and the system loops on the
interrupt handler.
To workaround this, introduce a WDC_NO_IDS compile option which runs
all polled commands (including reset) at splbio() and without sleeps,
so that the controller's interrupt is effectively disabled and
won't be reenabled before the interrupt can be cleared.
The conditions triggering this problem are speficic enough to handle
this via a compile-time option; no need for a run-time (e.g. a
config(9), device property or callback to disable interrupts) solution.
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