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>

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 41c69469ce2000ec223170970c856a2287f10db2..559d80335446ffcdfe7a9bcf86ee939f0be5fb96 100644 (file)
--- 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

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index fbd9ccd5e114ccdf1eb2db91499315689f6ed407..105f8ffa66a8413cb0131ae001acba23b8b6ea8d 100644 (file)
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -294,6 +294,19 @@ static void __arch_timer_setup(unsigned type,
        clockevents_config_and_register(clk, arch_timer_rate, 0xf, 0x7fffffff);
 }
 
+static void arch_timer_configure_evtstream(void)
+{
+       int evt_stream_div, pos;
+
+       /* Find the closest power of two to the divisor */
+       evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
+       pos = fls(evt_stream_div);
+       if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
+               pos--;
+       /* enable event stream */
+       arch_timer_evtstrm_enable(min(pos, 15));
+}
+
 static int arch_timer_setup(struct clock_event_device *clk)
 {
        __arch_timer_setup(ARCH_CP15_TIMER, clk);
@@ -307,6 +320,8 @@ static int arch_timer_setup(struct clock_event_device *clk)
        }
 
        arch_counter_set_user_access();
+       if (IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM))
+               arch_timer_configure_evtstream();
 
        return 0;
 }

diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
index 8707dae4cee264653864ff27d76bd4967795b945..6d26b40cbf5d29c7d80c83a9fe22b4f9e85a0b70 100644 (file)
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -41,6 +41,8 @@ enum arch_timer_reg {
 #define ARCH_TIMER_USR_VT_ACCESS_EN    (1 << 8) /* virtual timer registers */
 #define ARCH_TIMER_USR_PT_ACCESS_EN    (1 << 9) /* physical timer registers */
 
+#define ARCH_TIMER_EVT_STREAM_FREQ     10000   /* 100us */
+
 #ifdef CONFIG_ARM_ARCH_TIMER
 
 extern u32 arch_timer_get_rate(void);