Suppress XSCOM chiplet-offline errors on P9

Workaround on P9: PRD does operations it *knows* will fail with this
error to work around a hardware issue where accesses via the PIB
(FSI or OCC) work as expected, accesses via the ADU (what xscom goes
through) do not. The chip logic will always return all FFs if there
is any error on the scom.

Suggested-by: Daniel M Crowell <dcrowell@us.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Acked-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

hw/xscom.c

@@ -1,4 +1,4 @@
-/* Copyright 2013-2014 IBM Corp.
+/* Copyright 2013-2017 IBM Corp.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -284,6 +284,16 @@ static int __xscom_read(uint32_t gcid, uint32_t pcb_addr, uint64_t *val)
 	if (xscom_is_multicast_addr(pcb_addr) && ret == OPAL_XSCOM_CHIPLET_OFF)
 		return ret;
 
+	/*
+	 * Workaround on P9: PRD does operations it *knows* will fail with this
+	 * error to work around a hardware issue where accesses via the PIB
+	 * (FSI or OCC) work as expected, accesses via the ADU (what xscom goes
+	 * through) do not. The chip logic will always return all FFs if there
+	 * is any error on the scom.
+	 */
+	if (proc_gen == proc_gen_p9 && ret == OPAL_XSCOM_CHIPLET_OFF)
+		return ret;
+
 	prerror("XSCOM: Read failed, ret =  %lld\n", ret);
 	return ret;
 }
@@ -324,6 +334,16 @@ static int __xscom_write(uint32_t gcid, uint32_t pcb_addr, uint64_t val)
 	if (xscom_is_multicast_addr(pcb_addr) && ret == OPAL_XSCOM_CHIPLET_OFF)
 		return ret;
 
+	/*
+	 * Workaround on P9: PRD does operations it *knows* will fail with this
+	 * error to work around a hardware issue where accesses via the PIB
+	 * (FSI or OCC) work as expected, accesses via the ADU (what xscom goes
+	 * through) do not. The chip logic will always return all FFs if there
+	 * is any error on the scom.
+	 */
+	if (proc_gen == proc_gen_p9 && ret == OPAL_XSCOM_CHIPLET_OFF)
+		return ret;
+
 	prerror("XSCOM: Write failed, ret =  %lld\n", ret);
 	return ret;
 }