powerpc/cpufreq: Add pr_warn() on OPAL firmware failures

Cpufreq depends on platform firmware to implement PStates.  In case of
platform firmware failure, cpufreq should not panic host kernel with
BUG_ON().  Less severe pr_warn() will suffice.

Add firmware_has_feature(FW_FEATURE_OPALv3) check to
skip probing for device-tree on non-powernv platforms.
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Acked-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/cpufreq/powernv-cpufreq.c

@@ -28,6 +28,7 @@
 #include <linux/of.h>
 
 #include <asm/cputhreads.h>
+#include <asm/firmware.h>
 #include <asm/reg.h>
 #include <asm/smp.h> /* Required for cpu_sibling_mask() in UP configs */
 
@@ -98,7 +99,11 @@ static int init_powernv_pstates(void)
 		return -ENODEV;
 	}
 
-	WARN_ON(len_ids != len_freqs);
+	if (len_ids != len_freqs) {
+		pr_warn("Entries in ibm,pstate-ids and "
+			"ibm,pstate-frequencies-mhz does not match\n");
+	}
+
 	nr_pstates = min(len_ids, len_freqs) / sizeof(u32);
 	if (!nr_pstates) {
 		pr_warn("No PStates found\n");
@@ -131,7 +136,12 @@ static unsigned int pstate_id_to_freq(int pstate_id)
 	int i;
 
 	i = powernv_pstate_info.max - pstate_id;
-	BUG_ON(i >= powernv_pstate_info.nr_pstates || i < 0);
+	if (i >= powernv_pstate_info.nr_pstates || i < 0) {
+		pr_warn("PState id %d outside of PState table, "
+			"reporting nominal id %d instead\n",
+			pstate_id, powernv_pstate_info.nominal);
+		i = powernv_pstate_info.max - powernv_pstate_info.nominal;
+	}
 
 	return powernv_freqs[i].frequency;
 }
@@ -321,6 +331,10 @@ static int __init powernv_cpufreq_init(void)
 {
 	int rc = 0;
 
+	/* Don't probe on pseries (guest) platforms */
+	if (!firmware_has_feature(FW_FEATURE_OPALv3))
+		return -ENODEV;
+
 	/* Discover pstates from device tree and init */
 	rc = init_powernv_pstates();
 	if (rc) {