From 46770be0cf94149ca48be87719bda1d951066644 Mon Sep 17 00:00:00 2001
From: Viresh Kumar <viresh.kumar@linaro.org>
Date: Thu, 14 Nov 2019 09:06:17 +0530
Subject: [PATCH] cpufreq: Register drivers only after CPU devices have been registered
Git-commit: 46770be0cf94149ca48be87719bda1d951066644
Patch-mainline: v5.5-rc1
References: bsc#1051510

The cpufreq core heavily depends on the availability of the struct
device for CPUs and if they aren't available at the time cpufreq driver
is registered, we will never succeed in making cpufreq work.

This happens due to following sequence of events:

- cpufreq_register_driver()
  - subsys_interface_register()
  - return 0; //successful registration of driver

... at a later point of time

- register_cpu();
  - device_register();
    - bus_probe_device();
      - sif->add_dev();
	- cpufreq_add_dev();
	  - get_cpu_device(); //FAILS
  - per_cpu(cpu_sys_devices, num) = &cpu->dev; //used by get_cpu_device()
  - return 0; //CPU registered successfully

Because the per-cpu variable cpu_sys_devices is set only after the CPU
device is regsitered, cpufreq will never be able to get it when
cpufreq_add_dev() is called.

This patch avoids this failure by making sure device structure of at
least CPU0 is available when the cpufreq driver is registered, else
return -EPROBE_DEFER.

Reported-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Co-developed-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/cpufreq/cpufreq.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 0a10cf9d0b1a..7fc1a686f2f6 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2637,6 +2637,13 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	if (cpufreq_disabled())
 		return -ENODEV;
 
+	/*
+	 * The cpufreq core depends heavily on the availability of device
+	 * structure, make sure they are available before proceeding further.
+	 */
+	if (!get_cpu_device(0))
+		return -EPROBE_DEFER;
+
 	if (!driver_data || !driver_data->verify || !driver_data->init ||
 	    !(driver_data->setpolicy || driver_data->target_index ||
 		    driver_data->target) ||
-- 
2.16.4