Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755238Ab3H1Kov (ORCPT ); Wed, 28 Aug 2013 06:44:51 -0400 Received: from service87.mimecast.com ([91.220.42.44]:48384 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752458Ab3H1Kol (ORCPT ); Wed, 28 Aug 2013 06:44:41 -0400 From: Sudeep KarkadaNagesha To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Sudeep.KarkadaNagesha@arm.com, Lorenzo Pieralisi , Will Deacon , Catalin Marinas , Thomas Gleixner , Daniel Lezcano , Will Deacon , Lorenzo Pieralisi , Sudeep KarkadaNagesha Subject: [PATCH v5 4/5] drivers: clocksource: add support for ARM architected timer event stream Date: Wed, 28 Aug 2013 11:44:48 +0100 Message-Id: <1377686689-30828-5-git-send-email-Sudeep.KarkadaNagesha@arm.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1377686689-30828-1-git-send-email-Sudeep.KarkadaNagesha@arm.com> References: <1377686689-30828-1-git-send-email-Sudeep.KarkadaNagesha@arm.com> X-OriginalArrivalTime: 28 Aug 2013 10:44:38.0704 (UTC) FILETIME=[98341B00:01CEA3DB] X-MC-Unique: 113082811444003101 Content-Type: text/plain; charset=WINDOWS-1252 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id r7SAiukS005371 Content-Length: 4060 Lines: 114 From: Will Deacon 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 impose a time-out on a wfe polling loop. - To safeguard against any programming error in case an expected event is not generated. - To implement wfe-based timeouts for userspace locking implementations. 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 Cc: Catalin Marinas Signed-off-by: Will Deacon [sudeep: moving ARM/ARM64 changes into separate patches and adding Kconfig option] Signed-off-by: Sudeep KarkadaNagesha --- drivers/clocksource/Kconfig | 14 ++++++++++++++ drivers/clocksource/arm_arch_timer.c | 21 +++++++++++++++++++++ include/clocksource/arm_arch_timer.h | 2 ++ 3 files changed, 37 insertions(+) diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index b7b9b04..74946ca 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -74,6 +74,20 @@ 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. An event stream might be useful for + imposing timeout on a wfe, safeguarding against any programming + errors in case an expected event is not generated or even to + implement wfe-based timeouts for userspace locking implementations. + This can 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 ffadd83..f42bef4 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -123,6 +123,26 @@ static int arch_timer_set_next_event_phys(unsigned long evt, return 0; } +#ifdef CONFIG_ARM_ARCH_TIMER_EVTSTREAM +static void arch_timer_setup_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_config(true, min(pos, 15)); +} +#else +static void arch_timer_setup_evtstream(void) +{ + arch_timer_evtstrm_config(false, 0); +} +#endif + static int arch_timer_setup(struct clock_event_device *clk) { clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP; @@ -154,6 +174,7 @@ static int arch_timer_setup(struct clock_event_device *clk) } arch_counter_set_user_access(); + arch_timer_setup_evtstream(); return 0; } diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h index 551f7e9..c4d0fc4 100644 --- a/include/clocksource/arm_arch_timer.h +++ b/include/clocksource/arm_arch_timer.h @@ -37,6 +37,8 @@ #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); -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/