Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756141Ab3H2LUS (ORCPT ); Thu, 29 Aug 2013 07:20:18 -0400 Received: from fw-tnat.cambridge.arm.com ([217.140.96.21]:52668 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752366Ab3H2LUQ (ORCPT ); Thu, 29 Aug 2013 07:20:16 -0400 Date: Thu, 29 Aug 2013 12:19:35 +0100 From: Catalin Marinas To: Sudeep KarkadaNagesha Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Lorenzo Pieralisi , Will Deacon , Thomas Gleixner , Daniel Lezcano Subject: Re: [PATCH v5 4/5] drivers: clocksource: add support for ARM architected timer event stream Message-ID: <20130829111935.GD13704@arm.com> References: <1377686689-30828-1-git-send-email-Sudeep.KarkadaNagesha@arm.com> <1377686689-30828-5-git-send-email-Sudeep.KarkadaNagesha@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1377686689-30828-5-git-send-email-Sudeep.KarkadaNagesha@arm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4104 Lines: 111 On Wed, Aug 28, 2013 at 11:44:48AM +0100, Sudeep KarkadaNagesha wrote: > 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. Maybe we should reorder this a bit and make the wfe-based timeouts as the main reason. > + > 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 I think we only need an arch_timer_evtstrm_enable() function without the bool argument. We don't need to disable it at run-time. > + > 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(); and here just: if (IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM)) arch_timer_evtstrm_enable(); -- Catalin -- 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/