sata_promise: SATA hotplug support, take 2

sata_promise: SATA hotplug support, take 2

This patch enables hotplugging of SATA devices in the
sata_promise driver. It's been tested successfully on
both first- and second-generation Promise SATA chips:
SATA150 TX2plus, SATAII150 TX2plus, SATAII150 TX4,
SATA300 TX2plus, and SATA300 TX4.

The only quirk I've seen is that hotplugging (insertion)
on the first-generation SATA150 TX2plus requires a lengthier
EH sequence than on the second-generation chips.
On the second-generation chips a simple soft reset seems
to suffice, but on the first-generation chip there's a
"port is slow to respond" after the initial soft reset,
after which libata issues a hard reset, and then the
device is recognised.

The hotplug checks are high up in the interrupt handling
path, not deep down in error_intr as in ahci/sata_sil24.
That's because the chip doesn't signal hotplug status changes
in the per-port status register: instead a global register
contains hotplug control and status flags for all ports.
I considered following the ahci/sata_sil24 structure, but
that would have required non-trivial changes to the interrupt
handling path, so I chose to keep the hotplug changes simple
and unobtrusive.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
--
This patch depends on the "sata_promise: cleanups" patch.

Changes since the previous version (posted June 19):
- Correct pdc_interrupt() to increment 'handled' also in
  the hotplug case. This prevents IRQ_NONE from being
  returned when an interrupt only has hotplug events to
  handle, which could confuse the kernel's IRQ machinery.
- Added testing on the SATAII150 TX4.

 drivers/ata/sata_promise.c |   41 ++++++++++++++++++++++++++++++++++++-----
 1 files changed, 36 insertions(+), 5 deletions(-)
Signed-off-by: Jeff Garzik <jeff@garzik.org>