[Skiboot] [PATCH v2] opal/xstop: Use nvram option 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'i for p9. 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.

For p8 platform it will remain enabled by default unless explicitly disabled.

To disable sw checkstop on p8 issue following command:

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

Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
Reviewed-by: Balbir Singh <bsingharora at gmail.com>
---
Change in v2:
   - Add pr_log to indicate that sw checkstop was disabled.
---
 hw/xscom.c |   32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/hw/xscom.c b/hw/xscom.c
index de5a27e..0501278 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 | \
@@ -826,6 +827,37 @@ static void xscom_init_chip_info(struct proc_chip *chip)
 int64_t xscom_trigger_xstop(void)
 {
 	int rc = OPAL_UNSUPPORTED;
+	bool xstop_disabled = false;
+
+	/*
+	 * Workaround until we iron out all checkstop issues at present.
+	 *
+	 * For p9:
+	 * By default do not trigger sw checkstop unless explicitly enabled
+	 * through nvram option 'opal-sw-xstop=enable'.
+	 *
+	 * For p8:
+	 * Keep it enabled by default unless explicitly disabled.
+	 *
+	 * NOTE: Once all checkstop issues are resolved/stabilized reverse
+	 * the logic to enable sw checkstop by default on p9.
+	 */
+	switch (proc_gen) {
+	case proc_gen_p8:
+		if (nvram_query_eq("opal-sw-xstop", "disable"))
+			xstop_disabled = true;
+		break;
+	case proc_gen_p9:
+	default:
+		if (!nvram_query_eq("opal-sw-xstop", "enable"))
+			xstop_disabled = true;
+		break;
+	}
+
+	if (xstop_disabled) {
+		prlog(PR_NOTICE, "Software initiated checkstop disabled.\n");
+		return rc;
+	}
 
 	if (xstop_xscom.addr)
 		rc = xscom_writeme(xstop_xscom.addr,