tools/power turbostat: Handle non-root legacy-uncore sysfs permissions

/sys/devices/system/cpu/intel_uncore_frequency/package_X_die_Y/
may be readable by all, but
/sys/devices/system/cpu/intel_uncore_frequency/package_X_die_Y/current_freq_khz
may be readable only by root.

Non-root turbostat users see complaints in this scenario.

Fail probe of the interface if we can't read current_freq_khz.

Reported-by: Artem Bityutskiy <[email protected]>
Original-patch-by: Zhang Rui <[email protected]>
Signed-off-by: Len Brown <[email protected]>

Author: lenb

tools/power/x86/turbostat/turbostat.c

@@ -7002,7 +7002,8 @@ static void probe_intel_uncore_frequency_legacy(void)
 			sprintf(path_base, "/sys/devices/system/cpu/intel_uncore_frequency/package_%02d_die_%02d", i,
 				j);
 
-			if (access(path_base, R_OK))
+			sprintf(path, "%s/current_freq_khz", path_base);
+			if (access(path, R_OK))
 				continue;
 
 			BIC_PRESENT(BIC_UNCORE_MHZ);