selftests/powerpc: Skip energy_scale_info test on older firmware

Older machines don't have the firmware feature that enables the code
this test is testing. Skip the test if the sysfs directory doesn't
exist. Also use the FAIL_IF() macro to provide more verbose error
reporting if an error is encountered.

Fixes: 57201d65 ("selftest/powerpc: Add PAPR sysfs attributes sniff test")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220619233103.2666171-1-mpe@ellerman.id.au

tools/testing/selftests/powerpc/papr_attributes/attr_test.c

@@ -7,6 +7,7 @@
  * Copyright 2022, Pratik Rajesh Sampat, IBM Corp.
  */
 
+#include <errno.h>
 #include <stdio.h>
 #include <string.h>
 #include <dirent.h>
@@ -32,7 +33,7 @@ enum type {
 	NUM_VAL
 };
 
-int value_type(int id)
+static int value_type(int id)
 {
 	int val_type;
 
@@ -54,15 +55,21 @@ int value_type(int id)
 	return val_type;
 }
 
-int verify_energy_info(void)
+static int verify_energy_info(void)
 {
 	const char *path = "/sys/firmware/papr/energy_scale_info";
 	struct dirent *entry;
 	struct stat s;
 	DIR *dirp;
 
-	if (stat(path, &s) || !S_ISDIR(s.st_mode))
-		return -1;
+	errno = 0;
+	if (stat(path, &s)) {
+		SKIP_IF(errno == ENOENT);
+		FAIL_IF(errno);
+	}
+
+	FAIL_IF(!S_ISDIR(s.st_mode));
+
 	dirp = opendir(path);
 
 	while ((entry = readdir(dirp)) != NULL) {
@@ -76,25 +83,24 @@ int verify_energy_info(void)
 
 		id = atoi(entry->d_name);
 		attr_type = value_type(id);
-		if (attr_type == INVALID)
-			return -1;
+		FAIL_IF(attr_type == INVALID);
 
 		/* Check if the files exist and have data in them */
 		sprintf(file_name, "%s/%d/desc", path, id);
 		f = fopen(file_name, "r");
-		if (!f || fgetc(f) == EOF)
-			return -1;
+		FAIL_IF(!f);
+		FAIL_IF(fgetc(f) == EOF);
 
 		sprintf(file_name, "%s/%d/value", path, id);
 		f = fopen(file_name, "r");
-		if (!f || fgetc(f) == EOF)
-			return -1;
+		FAIL_IF(!f);
+		FAIL_IF(fgetc(f) == EOF);
 
 		if (attr_type == STR_VAL) {
 			sprintf(file_name, "%s/%d/value_desc", path, id);
 			f = fopen(file_name, "r");
-			if (!f || fgetc(f) == EOF)
-				return -1;
+			FAIL_IF(!f);
+			FAIL_IF(fgetc(f) == EOF);
 		}
 	}