ACPI / PM: Leave Bus Master Arbitration enabled for suspend/resume

This is an old suspend/resume lockup fix:

	commit 2780cc4660e1
	Author: Len Brown <len.brown@intel.com>
	Date:   Thu Dec 23 13:43:30 2004 -0500

	    [ACPI] Fix suspend/resume lockup issue
	    by leaving Bus Master Arbitration enabled.
	    The ACPI spec mandates it be disabled only for C3.

	    http://bugzilla.kernel.org/show_bug.cgi?id=3599

	    Signed-off-by: David Shaohua Li <shaohua.li@intel.com>
	    Signed-off-by: Len Brown <len.brown@intel.com>

The bug snuck back in in commit 2feec47 (ACPICA: ACPI 5: Support
for new FADT SleepStatus, SleepControl registers, 2012-02-14),
presumably by copy/pasting a copy of the code without that fix for the
legacy case.

On affected machines, after that commit, the machine locks up hard on
resume from suspend.  The same fix as seven years ago still works.

Addresses <https://bugzilla.kernel.org/show_bug.cgi?id=43641>.

Reported-bisected-and-tested-by: Octavio Alvarez <alvarezp@alvarezp.com>
Reported-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

drivers/acpi/acpica/hwsleep.c

@@ -95,18 +95,6 @@ acpi_status acpi_hw_legacy_sleep(u8 sleep_state, u8 flags)
 		return_ACPI_STATUS(status);
 	}
 
-	if (sleep_state != ACPI_STATE_S5) {
-		/*
-		 * Disable BM arbitration. This feature is contained within an
-		 * optional register (PM2 Control), so ignore a BAD_ADDRESS
-		 * exception.
-		 */
-		status = acpi_write_bit_register(ACPI_BITREG_ARB_DISABLE, 1);
-		if (ACPI_FAILURE(status) && (status != AE_BAD_ADDRESS)) {
-			return_ACPI_STATUS(status);
-		}
-	}
-
 	/*
 	 * 1) Disable/Clear all GPEs
 	 * 2) Enable all wakeup GPEs
@@ -364,16 +352,6 @@ acpi_status acpi_hw_legacy_wake(u8 sleep_state, u8 flags)
 				    [ACPI_EVENT_POWER_BUTTON].
 				    status_register_id, ACPI_CLEAR_STATUS);
 
-	/*
-	 * Enable BM arbitration. This feature is contained within an
-	 * optional register (PM2 Control), so ignore a BAD_ADDRESS
-	 * exception.
-	 */
-	status = acpi_write_bit_register(ACPI_BITREG_ARB_DISABLE, 0);
-	if (ACPI_FAILURE(status) && (status != AE_BAD_ADDRESS)) {
-		return_ACPI_STATUS(status);
-	}
-
 	acpi_hw_execute_sleep_method(METHOD_PATHNAME__SST, ACPI_SST_WORKING);
 	return_ACPI_STATUS(status);
 }