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Date: Mon, 12 Aug 2013 14:32:18 +0100
From: Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To: Catalin Marinas <Catalin.Marinas@....com>
CC: Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Mark Rutland <Mark.Rutland@....com>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
Russell King <linux@....linux.org.uk>,
Will Deacon <Will.Deacon@....com>,
Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v3 1/3] drivers: clocksource: configure event stream for
ARM arch timer
On 25/07/13 10:45, Sudeep KarkadaNagesha wrote:
> From: Will Deacon <will.deacon@....com>
>
> 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.
>
> This patch configures the event stream, aiming for a period of 100us
> between events. This can be used to implement wfe-based timeouts for
> userspace locking implementations.
>
> This patch also adds the hwcaps for the same, so that userspace can
> detect this feature.
>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
> arch/arm/include/asm/arch_timer.h | 6 ++++--
> arch/arm/include/uapi/asm/hwcap.h | 1 +
> arch/arm/kernel/setup.c | 1 +
> arch/arm64/include/asm/arch_timer.h | 6 +++---
> drivers/clocksource/arm_arch_timer.c | 9 ++++++++-
> include/clocksource/arm_arch_timer.h | 2 ++
> 6 files changed, 19 insertions(+), 6 deletions(-)
>
> ------------>8---------------------
>
> Hi,
>
> This version adds the hwcaps for publishing the event stream feature to the
> userspace.
>
Hi Catalin,
If you are OK with this patch, can I have your ACK ?
Regards,
Sudeep
> This patch is now rebased on rmk's fixes branch as it conflicts with ab8d46c0
> "ARM: 7788/1: elf: fix lpae hwcap feature reporting in proc/cpuinfo"
>
> Regards,
> Sudeep
>
> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
> index e406d57..8963877 100644
> --- a/arch/arm/include/asm/arch_timer.h
> +++ b/arch/arm/include/asm/arch_timer.h
> @@ -89,16 +89,18 @@ static inline u64 arch_counter_get_cntvct(void)
> return cval;
> }
>
> -static inline void arch_counter_set_user_access(void)
> +static inline void arch_counter_set_user_access(int divider)
> {
> u32 cntkctl;
>
> asm volatile("mrc p15, 0, %0, c14, c1, 0" : "=r" (cntkctl));
>
> /* disable user access to everything */
> - cntkctl &= ~((3 << 8) | (7 << 0));
> + cntkctl &= ~((3 << 8) | (0xf << 4) | (3 << 0));
> + cntkctl |= (divider << 4) | (1 << 2);
>
> asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl));
> + elf_hwcap |= HWCAP_EVTSTRM;
> }
> #endif
>
> diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h
> index 6d34d08..7dcc10d 100644
> --- a/arch/arm/include/uapi/asm/hwcap.h
> +++ b/arch/arm/include/uapi/asm/hwcap.h
> @@ -26,5 +26,6 @@
> #define HWCAP_VFPD32 (1 << 19) /* set if VFP has 32 regs (not 16) */
> #define HWCAP_IDIV (HWCAP_IDIVA | HWCAP_IDIVT)
> #define HWCAP_LPAE (1 << 20)
> +#define HWCAP_EVTSTRM (1 << 21)
>
> #endif /* _UAPI__ASMARM_HWCAP_H */
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 96286cb..5191956 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -973,6 +973,7 @@ static const char *hwcap_str[] = {
> "idivt",
> "vfpd32",
> "lpae",
> + "evtstrm",
> NULL
> };
>
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index 98abd47..8c1e42f 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -97,16 +97,16 @@ static inline u32 arch_timer_get_cntfrq(void)
> return val;
> }
>
> -static inline void arch_counter_set_user_access(void)
> +static inline void arch_counter_set_user_access(int divider)
> {
> u32 cntkctl;
>
> /* Disable user access to the timers and the physical counter. */
> asm volatile("mrs %0, cntkctl_el1" : "=r" (cntkctl));
> - cntkctl &= ~((3 << 8) | (1 << 0));
> + cntkctl &= ~((3 << 8) | (0xf << 4) | (1 << 0));
>
> /* Enable user access to the virtual counter and frequency. */
> - cntkctl |= (1 << 1);
> + cntkctl |= (divider << 4) | (1 << 2) | (1 << 1);
> asm volatile("msr cntkctl_el1, %0" : : "r" (cntkctl));
> }
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index ffadd83..6301ee5 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -125,6 +125,8 @@ static int arch_timer_set_next_event_phys(unsigned long evt,
>
> static int arch_timer_setup(struct clock_event_device *clk)
> {
> + int evt_stream_div, pos;
> +
> clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP;
> clk->name = "arch_sys_timer";
> clk->rating = 450;
> @@ -153,7 +155,12 @@ static int arch_timer_setup(struct clock_event_device *clk)
> enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], 0);
> }
>
> - arch_counter_set_user_access();
> + /* 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--;
> + arch_counter_set_user_access(min(pos, 15));
>
> return 0;
> }
> diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
> index c463ce9..24dc140 100644
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -29,6 +29,8 @@
> #define ARCH_TIMER_PHYS_ACCESS 0
> #define ARCH_TIMER_VIRT_ACCESS 1
>
> +#define ARCH_TIMER_EVT_STREAM_FREQ 10000 /* 100us */
> +
> #ifdef CONFIG_ARM_ARCH_TIMER
>
> extern u32 arch_timer_get_rate(void);
>
--
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