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Commit c509311d authored by Will Deacon's avatar Will Deacon Committed by Trilok Soni
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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.

Change-Id: I43906fa7d083a2c611c2047e15c34d68bb047ac7
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Acked-by: default avatarOlof Johansson <olof@lixom.net>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
[sudeep: moving ARM/ARM64 changes into separate patches
         and adding Kconfig option]
Signed-off-by: default avatarSudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
Git-commit: 37f637767a82907efedda78d3ff405c34020075
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[tsoni@codeaurora.org: Fixed trivial merge conflicts]
Signed-off-by: default avatarTrilok Soni <tsoni@codeaurora.org>
parent e4d39e9e

drivers/clocksource/Kconfig

+15 −0
Original line number Diff line number Diff line
@@ -67,6 +67,21 @@ 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 CLKSRC_METAG_GENERIC

	def_bool y if METAG

	help

drivers/clocksource/arm_arch_timer.c

+16 −1
Original line number Diff line number Diff line
@@ -325,7 +325,20 @@ static void arch_counter_set_user_access(void) 
	arch_timer_set_cntkctl(cntkctl);

}



static int __cpuinit arch_timer_setup(struct clock_event_device *clk)

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);
@@ -338,6 +351,8 @@ static int __cpuinit 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;

}

include/clocksource/arm_arch_timer.h

+2 −0
Original line number Diff line number Diff line
@@ -39,6 +39,8 @@ 
#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);