opal/hmi: set a flag to inform OS that TOD/TB has failed.

Set a flag to indicate OS about TOD/TB failure as part of new
opal_handle_hmi2 handler. This flag then can be used by OS to make sure
functions depending on TB value (e.g. udelay()) are aware of TB not
ticking.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

Author: maheshsal

core/hmi.c

@@ -1223,10 +1223,12 @@ static int handle_tfac_errors(struct OpalHMIEvent *hmi_evt, uint64_t *out_flags)
 	/* Set the TB state looking at TFMR register before we head out. */
 	this_cpu()->tb_invalid = !(mfspr(SPR_TFMR) & SPR_TFMR_TB_VALID);
 
-	if (this_cpu()->tb_invalid)
+	if (this_cpu()->tb_invalid) {
+		*out_flags |= OPAL_HMI_FLAGS_TOD_TB_FAIL;
 		prlog(PR_WARNING, "Failed to get TB in running state! "
 			"CPU=%x, TFMR=%016lx\n", this_cpu()->pir,
 					mfspr(SPR_TFMR));
+	}
 
 	return recover;
 }

doc/opal-api/opal-handle-hmi-98-166.rst

@@ -93,7 +93,14 @@ OPAL_HANDLE_HMI and OPAL_HANDLE_HMI2
   is an old interface. ```OPAL_HANDLE_HMI2``` is newly introduced opal call
   that returns direct info to Linux. It returns a 64-bit flag mask currently
   set to provide info about which timer facilities were lost, and whether an
-  event was generated.
+  event was generated. This information will help OS to take respective
+  actions.
+
+  In case where opal hmi handler is unable to recover from TOD or TB errors,
+  it would flag ```OPAL_HMI_FLAGS_TOD_TB_FAIL``` to indicate OS that TB is
+  dead. This information then can be used by OS to make sure that the
+  functions relying on TB value (e.g. udelay()) are aware of TB not ticking.
+  This will avoid OS getting stuck or hang during its way to panic path.
 
 OPAL_HANDLE_HMI
 ---------------
@@ -122,5 +129,6 @@ parameters
         OPAL_HMI_FLAGS_TB_RESYNC        = (1ull << 0), /* Timebase has been resynced */
         OPAL_HMI_FLAGS_DEC_LOST         = (1ull << 1), /* DEC lost, needs to be reprogrammed */
         OPAL_HMI_FLAGS_HDEC_LOST        = (1ull << 2), /* HDEC lost, needs to be reprogrammed */
+        OPAL_HMI_FLAGS_TOD_TB_FAIL      = (1ull << 3), /* TOD/TB recovery failed. */
         OPAL_HMI_FLAGS_NEW_EVENT        = (1ull << 63), /* An event has been created */
    };

include/opal-api.h

@@ -777,6 +777,7 @@ enum {
 	OPAL_HMI_FLAGS_TB_RESYNC	= (1ull << 0), /* Timebase has been resynced */
 	OPAL_HMI_FLAGS_DEC_LOST		= (1ull << 1), /* DEC lost, needs to be reprogrammed */
 	OPAL_HMI_FLAGS_HDEC_LOST	= (1ull << 2), /* HDEC lost, needs to be reprogrammed */
+	OPAL_HMI_FLAGS_TOD_TB_FAIL	= (1ull << 3), /* TOD/TB recovery failed. */
 	OPAL_HMI_FLAGS_NEW_EVENT	= (1ull << 63), /* An event has been created */
 };