pmdomain: arm: Fix NULL dereference on scmi_perf_domain removal

On unloading of the scmi_perf_domain module got the below splat, when in
the DT provided to the system under test the '#power-domain-cells' property
was missing. Indeed, this particular setup causes the probe to bail out
early without giving any error, which leads to the ->remove() callback gets
to run too, but without all the expected initialized structures in place.

Add a check and bail out early on remove too.

Call trace:
scmi_perf_domain_remove+0x28/0x70 [scmi_perf_domain]
scmi_dev_remove+0x28/0x40 [scmi_core]
device_remove+0x54/0x90
device_release_driver_internal+0x1dc/0x240
driver_detach+0x58/0xa8
bus_remove_driver+0x78/0x108
driver_unregister+0x38/0x70
scmi_driver_unregister+0x28/0x180 [scmi_core]
scmi_perf_domain_driver_exit+0x18/0xb78 [scmi_perf_domain]
__arm64_sys_delete_module+0x1a8/0x2c0
invoke_syscall+0x50/0x128
el0_svc_common.constprop.0+0x48/0xf0
do_el0_svc+0x24/0x38
el0_svc+0x34/0xb8
el0t_64_sync_handler+0x100/0x130
el0t_64_sync+0x190/0x198
Code: a90153f3 f9403c14 f9414800 955f8a05 (b9400a80)
---[ end trace 0000000000000000 ]---

Fixes: 2af23ceb8624 ("pmdomain: arm: Add the SCMI performance domain")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240125191756.868860-1-cristian.marussi@arm.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

pmdomain: arm: Avoid polling for scmi_perf_domain

It was a mistake to prefer polling based mode when setting a performance
level for a domain. Let's instead rely on the protocol to decide what is
best and thus avoid polling when possible.

Reported-by: Nikunj Kela <nkela@quicinc.com>
Fixes: 2af23ceb8624 ("pmdomain: arm: Add the SCMI performance domain")
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20231127135033.136442-1-ulf.hansson@linaro.org

firmware: arm_scmi: Add generic OPP support to the SCMI performance domain

To allow a consumer driver to use the OPP library to scale the performance
for its device, let's dynamically add the OPP table when the device gets
attached to its SCMI performance domain.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20230925131715.138411-10-ulf.hansson@linaro.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

pmdomain: arm: Add the SCMI performance domain

To enable support for performance scaling (DVFS) for generic devices with
the SCMI performance protocol, let's add an SCMI performance domain. This
is being modelled as a genpd provider, with support for performance scaling
through genpd's ->set_performance_state() callback.

Note that, this adds the initial support that allows consumer drivers for
attached devices, to vote for a new performance state via calling the
dev_pm_genpd_set_performance_state(). However, this should be avoided as
it's in most cases preferred to use the OPP library to vote for a new OPP
instead. The support using the OPP library isn't part of this change, but
needs to be implemented from subsequent changes.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20230919121605.7304-1-ulf.hansson@linaro.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>