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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>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.