cpufreq: cpu0: OPPs can be populated at runtime

OPPs can be populated statically, via DT, or added at run time with
dev_pm_opp_add().

While this driver handles the first case correctly, it would fail to populate
OPPs added at runtime. Because call to of_init_opp_table() would fail as there
are no OPPs in DT and probe will return early.

To fix this, remove error checking and call dev_pm_opp_init_cpufreq_table()
unconditionally.

Update bindings as well.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Tested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt

@@ -8,10 +8,12 @@ Both required and optional properties listed below must be defined
 under node /cpus/cpu@0.
 
 Required properties:
-- operating-points: Refer to Documentation/devicetree/bindings/power/opp.txt
-  for details
+- None
 
 Optional properties:
+- operating-points: Refer to Documentation/devicetree/bindings/power/opp.txt for
+  details. OPPs *must* be supplied either via DT, i.e. this property, or
+  populated at runtime.
 - clock-latency: Specify the possible maximum transition latency for clock,
   in unit of nanoseconds.
 - voltage-tolerance: Specify the CPU voltage tolerance in percentage.

drivers/cpufreq/cpufreq-cpu0.c

@@ -152,11 +152,8 @@ static int cpu0_cpufreq_probe(struct platform_device *pdev)
 		goto out_put_reg;
 	}
 
-	ret = of_init_opp_table(cpu_dev);
-	if (ret) {
-		pr_err("failed to init OPP table: %d\n", ret);
-		goto out_put_clk;
-	}
+	/* OPPs might be populated at runtime, don't check for error here */
+	of_init_opp_table(cpu_dev);
 
 	ret = dev_pm_opp_init_cpufreq_table(cpu_dev, &freq_table);
 	if (ret) {