[Skiboot] [RFC PATCH] opal/xstop: Use nvram param to enable/disable sw checkstop.

[Mahesh J Salgaonkar]

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

Add a mechanism to enable/disable sw checkstop by looking at nvram option
opal-sw-xstop=<enable/disable>.

For now this patch disables the sw checkstop trigger unless explicitly
enabled through nvram option 'opal-sw-xstop=enable'. This will allow an
opportunity to get host kernel in panic path or xmon for unrecoverable
HMIs or MCE, to be able to debug the issue effectively.

To enable sw checkstop in opal issue following command:

# nvram -p ibm,skiboot --update-config opal-sw-xstop=enable

NOTE: This is a workaround patch to disable sw checkstop by default to gain
control in host kernel for better checkstop debugging. Once we have most of
the checkstop issues stabilized/resolved, revisit this patch to enable sw
checkstop by default.

Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
---
 hw/xscom.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/hw/xscom.c b/hw/xscom.c
index de5a27e..4d3d88f 100644
--- a/hw/xscom.c
+++ b/hw/xscom.c
@@ -24,6 +24,7 @@
 #include <errorlog.h>
 #include <opal-api.h>
 #include <timebase.h>
+#include <nvram.h>
 
 /* Mask of bits to clear in HMER before an access */
 #define HMER_CLR_MASK	(~(SPR_HMER_XSCOM_FAIL | \
@@ -827,6 +828,18 @@ int64_t xscom_trigger_xstop(void)
 {
 	int rc = OPAL_UNSUPPORTED;
 
+	/*
+	 * Workaround until we iron out all checkstop issues at present.
+	 *
+	 * By deafult do not trigger sw checkstop unless explicitly enabled
+	 * through nvram option 'opal-sw-xstop=enable'.
+	 *
+	 * NOTE: Once all checkstop issues are resolved/stabilized reverse
+	 * the logic to enable sw checkstop by default.
+	 */
+	if (!nvram_query_eq("opal-sw-xstop", "enable"))
+		return rc;
+
 	if (xstop_xscom.addr)
 		rc = xscom_writeme(xstop_xscom.addr,
 				PPC_BIT(xstop_xscom.fir_bit));