clocksource/arm_arch_timer: Add basic ARMv8.6 support

This is v3 of the series enabling ARMv8.6 support for timer subsystem,
and was prompted by a discussion with Oliver around the fact that an
ARMv8.6 implementation must have a 1GHz counter, which leads to a
number of things to break in the timer code:

- the counter rollover can come pretty quickly as we only advertise a
  56bit counter,
- the maximum timer delta can be remarkably small, as we use the
  countdown interface which is limited to 32bit...

Thankfully, there is a way out: we can compute the minimal width of
the counter based on the guarantees that the architecture gives us,
and we can use the 64bit comparator interface instead of the countdown
to program the timer.

Finally, we start making use of the ARMv8.6 ECV features by switching
accesses to the counters to a self-synchronising register, removing
the need for an ISB. Hopefully, implementations will *not* just stick
an invisible ISB there...

A side effect of the switch to CVAL is that XGene-1 breaks. I have
added a workaround to keep it alive.

I have added Oliver's original patch[0] to the series and tweaked a
couple of things. Blame me if I broke anything.

The whole things has been tested on Juno (sysreg + MMIO timers),
XGene-1 (broken sysreg timers), FVP (FEAT_ECV, CNT*CTSS_EL0).

* From v2 [2]:
  - New patch adding a HWCAP (ECV) allowing userspace to probe for
    the presence of CNTVSS_EL0.

* From v1 [1]:
  - New patch adding a bunch of BUILD_BUG()s for register accesses we
    don't expect. This makes subsequent patches much simpler.
  - New patch moving the ISBs for workaround in a way that makes
    more sense for the self-synchronising accessors.
  - Rework the XGene-1 workaround to rely solely on MIDR.
  - Split the CNTVCTSS trap handling in its own patch.
  - Rebased on 5.15-rc2
  - Collected RBs, with thanks.

[0] https://lore.kernel.org/r/20210807191428.3488948-1-oupton...
[1] https://lore.kernel.org/r/20210809152651.2297337-2-maz@ke...
[2] https://lore.kernel.org/r/20210922211941.2756270-1-maz@ke...

Marc Zyngier (16):
  clocksource/arm_arch_timer: Add build-time guards for unhandled
    register accesses
  clocksource/arm_arch_timer: Drop CNT*_TVAL read accessors
  clocksource/arm_arch_timer: Extend write side of timer register
    accessors to u64
  clocksource/arm_arch_timer: Move system register timer programming
    over to CVAL
  clocksource/arm_arch_timer: Move drop _tval from erratum function
    names
  clocksource/arm_arch_timer: Fix MMIO base address vs callback ordering
    issue
  clocksource/arm_arch_timer: Move MMIO timer programming over to CVAL
  clocksource/arm_arch_timer: Advertise 56bit timer to the core code
  clocksource/arm_arch_timer: Work around broken CVAL implementations
  clocksource/arm_arch_timer: Remove any trace of the TVAL programming
    interface
  clocksource/arm_arch_timer: Drop unnecessary ISB on CVAL programming
  clocksource/arch_arm_timer: Move workaround synchronisation around
  arm64: Add a capability for FEAT_ECV
  arm64: Add CNT{P,V}CTSS_EL0 alternatives to cnt{p,v}ct_el0
  arm64: Add handling of CNTVCTSS traps
  arm64: Add HWCAP for self-synchronising virtual counter

Oliver Upton (1):
  clocksource/arm_arch_timer: Fix masking for high freq counters

 Documentation/arm64/elf_hwcaps.rst   |   4 +
 arch/arm/include/asm/arch_timer.h    |  37 ++--
 arch/arm64/include/asm/arch_timer.h  |  78 +++++----
 arch/arm64/include/asm/esr.h         |   6 +
 arch/arm64/include/asm/hwcap.h       |   1 +
 arch/arm64/include/asm/sysreg.h      |   3 +
 arch/arm64/include/uapi/asm/hwcap.h  |   1 +
 arch/arm64/kernel/cpufeature.c       |  13 +-
 arch/arm64/kernel/cpuinfo.c          |   1 +
 arch/arm64/kernel/traps.c            |  11 ++
 arch/arm64/tools/cpucaps             |   1 +
 drivers/clocksource/arm_arch_timer.c | 243 ++++++++++++++++-----------
 include/clocksource/arm_arch_timer.h |   2 +-
 13 files changed, 254 insertions(+), 147 deletions(-)

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2.30.2