drivers: clocksource: add support for ARM architected timer event stream

The ARM architected timer can generate events (used for waking up
CPUs executing the wfe instruction) at a frequency represented as a
power-of-2 divisor of the clock rate.

An event stream might be used:
- To implement wfe-based timeouts for userspace locking implementations.
- To impose a timeout on a wfe for safeguarding against any programming
  error in case an expected event is not generated.

This patch computes the event stream frequency aiming for a period
of 100us between events. It uses ARM/ARM64 specific backends to configure
and enable the event stream.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>
[sudeep: moving ARM/ARM64 changes into separate patches
         and adding Kconfig option]
Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 41c69469ce20..559d80335446 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -74,6 +74,21 @@ config ARM_ARCH_TIMER
         bool
         select CLKSRC_OF if OF
 
+config ARM_ARCH_TIMER_EVTSTREAM
+        bool "Support for ARM architected timer event stream generation"
+        default y if ARM_ARCH_TIMER
+        help
+          This option enables support for event stream generation based on
+          the ARM architected timer. It is used for waking up CPUs executing
+          the wfe instruction at a frequency represented as a power-of-2
+          divisor of the clock rate.
+          The main use of the event stream is wfe-based timeouts of userspace
+          locking implementations. It might also be useful for imposing timeout
+          on wfe to safeguard against any programming errors in case an expected
+          event is not generated.
+          This must be disabled for hardware validation purposes to detect any
+          hardware anomalies of missing events.
+
 config ARM_GLOBAL_TIMER
         bool
         select CLKSRC_OF if OF