The ARMv7 architecture does not guarantee that effects from co-processor
writes are immediately visible to following instructions.

This patch adds two isbs to the ARMv7 perf code:

(1) Immediately after selecting an event register, so that the PMU state
    following this instruction is consistent with the new event.

(2) Immediately before writing to the PMCR, so that any previous writes
    to the PMU have taken effect before (typically) enabling the
    counters.
Acked-by: NJean Pihet <j-pihet@ti.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

For kernels built with PREEMPT_RT, critical sections protected
by standard spinlocks are preemptible. This is not acceptable
on perf as (a) we may be scheduled onto a different CPU whilst
reading/writing banked PMU registers and (b) the latency when
reading the PMU registers becomes unpredictable.

This patch upgrades the pmu_lock spinlock to a raw_spinlock
instead.
Reported-by: NJamie Iles <jamie@jamieiles.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Russell reported a number of warnings coming from sparse when
checking the ARM perf_event.c files:

| perf_event.c seems to also have problems too:
|
|   CHECK   arch/arm/kernel/perf_event.c
|   arch/arm/kernel/perf_event.c:37:1: warning: symbol 'pmu_lock' was not declared. Should it be static?
|   arch/arm/kernel/perf_event.c:70:1: warning: symbol 'cpu_hw_events' was not declared. Should it be static?
|   arch/arm/kernel/perf_event.c:1006:1: warning: symbol 'armv6pmu_enable_event' was not declared. Should it be static?
|   arch/arm/kernel/perf_event.c:1113:1: warning: symbol 'armv6pmu_stop' was not declared. Should it be static?
|   arch/arm/kernel/perf_event.c:1956:6: warning: symbol 'armv7pmu_enable_event' was not declared. Should it be static?
|   arch/arm/kernel/perf_event.c:3072:14: warning: incorrect type in argument 1 (different address spaces)
|   arch/arm/kernel/perf_event.c:3072:14:    expected void const volatile [noderef] <asn:1>*<noident>
|   arch/arm/kernel/perf_event.c:3072:14:    got struct frame_tail *tail
|   arch/arm/kernel/perf_event.c:3074:49: warning: incorrect type in argument 2 (different address spaces)
|   arch/arm/kernel/perf_event.c:3074:49:    expected void const [noderef] <asn:1>*from
|   arch/arm/kernel/perf_event.c:3074:49:    got struct frame_tail *tail

This patch resolves these issues so we can live in silence
again.
Reported-by: NRussell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

The ARM perf_event.c file contains all PMU backends and, as new PMUs
are introduced, will continue to grow.

This patch follows the example of x86 and splits the PMU implementations
into separate files which are then #included back into the main
file. Compile-time guards are added to each PMU file to avoid compiling
in code that is not relevant for the version of the architecture which
we are targetting.
Acked-by: NJean Pihet <j-pihet@ti.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>