[PATCH] powerpc/powernv: Fallback to old HMI handling behavior for old firmware

[Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com>]

From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

Recently we moved HMI handling into Linux kernel instead of taking
HMI directly in OPAL. This new change is dependent on new OPAL call
for HMI recovery which was introduced in newer firmware. While this new
change works fine with latest OPAL firmware, we broke the HMI handling
if we run newer kernel on old OPAL firmware that results in system hang.

This patch fixes this issue by falling back to old HMI behavior on older
OPAL firmware.

This patch introduces a check for opal token OPAL_HANDLE_HMI to see
if we are running on newer firmware or old firmware. On newer firmware
this check would return OPAL_TOKEN_PRESENT, otherwise we are running on
old firmware and fallback to old HMI behavior.

This patch depends on opal check token patch posted at ppc-devel
https://lists.ozlabs.org/pipermail/linuxppc-dev/2014-August/120224.html

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
---
 arch/powerpc/platforms/powernv/opal.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
index b44eec3..2768cd3 100644
--- a/arch/powerpc/platforms/powernv/opal.c
+++ b/arch/powerpc/platforms/powernv/opal.c
@@ -194,6 +194,24 @@ static int __init opal_register_exception_handlers(void)
 	 * fwnmi area at 0x7000 to provide the glue space to OPAL
 	 */
 	glue = 0x7000;
+
+	/* Check if we are running on newer firmware that exports
+	 * OPAL_HANDLE_HMI token. If yes, then don't ask opal to patch
+	 * HMI interrupt and we catch it directly in Linux kernel.
+	 *
+	 * For older firmware we will fallback to old behavior and
+	 * let OPAL patch the HMI vector and handle it inside OPAL
+	 * firmware.
+	 */
+	if (opal_check_token(OPAL_HANDLE_HMI) != OPAL_TOKEN_PRESENT) {
+		/* We are on old firmware. fallback to old behavior. */
+		pr_info("%s: Falling back to old HMI handling behavior.\n",
+			__func__);
+		opal_register_exception_handler(
+				OPAL_HYPERVISOR_MAINTENANCE_HANDLER,
+				0, glue);
+		glue += 128;
+	}
 	opal_register_exception_handler(OPAL_SOFTPATCH_HANDLER, 0, glue);
 #endif