cpufreq: apple-soc: Fix an IS_ERR() vs NULL check

The of_iomap() function returns NULL if it fails. It never returns
error pointers. Fix the check accordingly.

Fixes: 6286bbb40576 ("cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

cpufreq: apple-soc: Switch to the lowest frequency on suspend

Without this, the CPUs are left in a random pstate. Since we don't
support deep idle yet (which powers down the CPUs), this results in
significantly increased idle power consumption in suspend.

Fixes: 6286bbb40576 ("cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states")
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

cpufreq: apple: remove duplicate intializer

When -Woverride-init is enabled, gcc notices that the .attr
field is initialized twice:

drivers/cpufreq/apple-soc-cpufreq.c:331:27: error: initialized field overwritten [-Werror=override-init]
331 | .attr = apple_soc_cpufreq_hw_attr,
| ^~~~~~~~~~~~~~~~~~~~~~~~~

Remove the first one, since this is not actually used.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states

This driver implements CPU frequency scaling for Apple Silicon SoCs,
including M1 (t8103), M1 Max/Pro/Ultra (t600x), and M2 (t8112).

Each CPU cluster has its own register set, and frequency management is
fully automated by the hardware; the driver only has to write one
register. There is boost frequency support, but the hardware will only
allow their use if only a subset of cores in a cluster are in
non-deep-idle. Since we don't support deep idle yet, these frequencies
are not achievable, but the driver supports them. They will remain
disabled in the device tree until deep idle is implemented, to avoid
confusing users.

This driver does not yet implement the memory controller performance
state tuning that usually accompanies higher CPU p-states. This will be
done in a future patch.

Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>