clocksource/drivers/arm_arch_timer: Control the evtstrm via the cmdline

Disabling the eventstream can be useful for both remotely debugging a
deployed production system and development of code using WFE-based
polling loops. Whilst this can currently be controlled via a Kconfig
option (CONFIG_ARM_ARCH_TIMER_EVTSTREAM), it's often desirable to toggle
the feature on the command line, so this patch adds a new command-line
option ("clocksource.arm_arch_timer.evtstrm") to do just that. The
default behaviour is determined based on CONFIG_ARM_ARCH_TIMER_EVTSTREAM.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82b42c958d1c..2c92f1df7c69 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -687,6 +687,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         [SPARC64] tick
                         [X86-64] hpet,tsc
 
+        clocksource.arm_arch_timer.evtstrm=
+                        [ARM,ARM64]
+                        Format: <bool>
+                        Enable/disable the eventstream feature of the ARM
+                        architected timer so that code using WFE-based polling
+                        loops can be debugged more effectively on production
+                        systems.
+
         clearcpuid=BITNUM [X86]
                         Disable CPUID feature X for the kernel. See
                         arch/x86/include/asm/cpufeatures.h for the valid bit