ide: Handle irq disabling consistently

ide_timer_expiry() disables interrupt at function entry when acquiring
hwif->lock. Before disabling the device interrupt it unlocks hwif->lock,
but interrupts stay disabled. After the call to disable_irq() interrupts
are disabled again, which is a pointless exercise.

After the device irq handler has been invoked with interrupts disabled,
hwif->lock is acquired again with spin_lock_irq() because the device irq
handler might have reenabled interrupts. This is not documented and
confusing for the casual reader.

Remove the redundant local_irq_disable() and add a comment which explains
why hwif->lock has to be reacquired with spin_lock_irq().

Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Acked-by: David S. Miller <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/ide/ide-io.c

···
 		spin_unlock(&hwif->lock);
 		/* disable_irq_nosync ?? */
 		disable_irq(hwif->irq);
-		/* local CPU only, as if we were handling an interrupt */
-		local_irq_disable();
+
 		if (hwif->polling) {
 			startstop = handler(drive);
 		} else if (drive_is_ready(drive)) {
···
 				startstop = ide_error(drive, "irq timeout",
 					hwif->tp_ops->read_status(hwif));
 		}
+		/* Disable interrupts again, `handler' might have enabled it */
 		spin_lock_irq(&hwif->lock);
 		enable_irq(hwif->irq);
 		if (startstop == ide_stopped && hwif->polling == 0) {