[PATCH 00/13] clocksource/arm_arch_timer: Add basic ARMv8.6 support

From: Marc Zyngier
Date: Mon Aug 09 2021 - 11:27:53 EST

This small series has been 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).

[0] https://lore.kernel.org/r/20210807191428.3488948-1-oupton@xxxxxxxxxx

Marc Zyngier (12):
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
clocksource/arm_arch_timer: Fix MMIO base address vs callback ordering
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
clocksource/arm_arch_timer: Drop unnecessary ISB on CVAL programming
arm64: Add a capability for FEAT_EVC
arm64: Add CNT{P,V}CTSS_EL0 alternatives to cnt{p,v}ct_el0

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

arch/arm/include/asm/arch_timer.h | 29 ++--
arch/arm64/include/asm/arch_timer.h | 65 +++----
arch/arm64/include/asm/esr.h | 6 +
arch/arm64/include/asm/sysreg.h | 3 +
arch/arm64/kernel/cpufeature.c | 10 ++
arch/arm64/kernel/traps.c | 11 ++
arch/arm64/tools/cpucaps | 1 +
drivers/clocksource/arm_arch_timer.c | 249 ++++++++++++++++-----------
include/clocksource/arm_arch_timer.h | 2 +-
9 files changed, 234 insertions(+), 142 deletions(-)