From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Thu, 12 Oct 2017 11:26:12 +0100 Subject: [PATCH v3 1/2] arm_arch_timer: Expose event stream status In-Reply-To: References: <1506682350-9023-1-git-send-email-julien.thierry@arm.com> <1506682350-9023-2-git-send-email-julien.thierry@arm.com> <88b96039-f0a5-879f-6f68-d30b09ab0cc7@arm.com> <20171012093010.GA7395@arm.com> Message-ID: <20171012102612.GB7395@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Oct 12, 2017 at 10:40:57AM +0100, Julien Thierry wrote: > > > On 12/10/17 10:30, Will Deacon wrote: > >On Thu, Oct 12, 2017 at 10:27:06AM +0100, Suzuki K Poulose wrote: > >>On 29/09/17 11:52, Julien Thierry wrote: > >>>The arch timer configuration for a CPU might get reset after suspending > >>>said CPU. > >>> > >>>In order to reliably use the event stream in the kernel (e.g. for delays), > >>>we keep track of the state where we can safely concider the event stream as > >> > >>nit: consider > >> > >>>properly configured. > >>> > >>>Signed-off-by: Julien Thierry > >>>Cc: Mark Rutland > >>>Cc: Marc Zyngier > >>>Cc: Russell King > >>>Cc: Catalin Marinas > >>>Cc: Will Deacon > >>>--- > >>> arch/arm/include/asm/arch_timer.h | 1 + > >>> arch/arm64/include/asm/arch_timer.h | 1 + > >>> drivers/clocksource/arm_arch_timer.c | 20 ++++++++++++++++++-- > >>> include/clocksource/arm_arch_timer.h | 6 ++++++ > >>> 4 files changed, 26 insertions(+), 2 deletions(-) > >>> > >>>diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h > >>>index d4ebf56..0b6e104 100644 > >>>--- a/arch/arm/include/asm/arch_timer.h > >>>+++ b/arch/arm/include/asm/arch_timer.h > >>>@@ -106,6 +106,7 @@ static inline u32 arch_timer_get_cntkctl(void) > >>> static inline void arch_timer_set_cntkctl(u32 cntkctl) > >>> { > >>> asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl)); > >>>+ isb(); > >>> } > >>> > >>> #endif > >>>diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h > >>>index a652ce0..bdedd8f 100644 > >>>--- a/arch/arm64/include/asm/arch_timer.h > >>>+++ b/arch/arm64/include/asm/arch_timer.h > >>>@@ -144,6 +144,7 @@ static inline u32 arch_timer_get_cntkctl(void) > >>> static inline void arch_timer_set_cntkctl(u32 cntkctl) > >>> { > >>> write_sysreg(cntkctl, cntkctl_el1); > >>>+ isb(); > >>> } > >>> > >>> static inline u64 arch_counter_get_cntpct(void) > >>>diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > >>>index fd4b7f6..47cf15e 100644 > >>>--- a/drivers/clocksource/arm_arch_timer.c > >>>+++ b/drivers/clocksource/arm_arch_timer.c > >>>@@ -77,6 +77,7 @@ struct arch_timer { > >>> static bool arch_counter_suspend_stop; > >>> static bool vdso_default = true; > >>> > >>>+static cpumask_t evtstrm_available; > >>> static bool evtstrm_enable = IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM); > >>> > >>> static int __init early_evtstrm_cfg(char *buf) > >>>@@ -740,6 +741,7 @@ static void arch_timer_evtstrm_enable(int divider) > >>> #ifdef CONFIG_COMPAT > >>> compat_elf_hwcap |= COMPAT_HWCAP_EVTSTRM; > >>> #endif > >>>+ cpumask_set_cpu(smp_processor_id(), &evtstrm_available); > >>> } > >>> > >>> static void arch_timer_configure_evtstream(void) > >>>@@ -864,6 +866,11 @@ u32 arch_timer_get_rate(void) > >>> return arch_timer_rate; > >>> } > >>> > >>>+bool arch_timer_evtstrm_available(void) > >>>+{ > >>>+ return !!cpumask_test_cpu(smp_processor_id(), &evtstrm_available); > >>>+} > >>>+ > >> > >>This could live in the header file as static inlin, if the evtstrm_available > >>is made global and could avoid a function call where it is used. > > > >You might need an EXPORT_SYMBOl as well if you go down that route. > > Hmmm, I'm not fond of making the cpu mask global. I understand you can avoid > the branch + ret of the function, but generally you want to check if the > event stream is present to know if you can use wfe and wake up, so I don't > think it might be used in a performance critical path. > > So I'm wondering, is it really worth it? I have no strong preference, but I think you'll need o EXPORT something either way so that delay and friends can be used from modules. Will