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SubjectRe: [RFC PATCH v3 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes
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On 5/14/19 7:01 AM, Ricardo Neri wrote:
> Instead of setting the timer period directly in hpet_set_periodic(), add a
> new helper function hpet_set_comparator() that only sets the accumulator
> and comparator. hpet_set_periodic() will only prepare the timer for
> periodic mode and leave the expiration programming to
> hpet_set_comparator().
>
> This new function can also be used by other components (e.g., the HPET-
> based hardlockup detector) which also need to configure HPET timers. Thus,
> add its declaration into the hpet header file.
>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: Andi Kleen <andi.kleen@intel.com>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Philippe Ombredanne <pombredanne@nexb.com>
> Cc: Kate Stewart <kstewart@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> Cc: Stephane Eranian <eranian@google.com>
> Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
> Cc: x86@kernel.org
> Originally-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> ---
> arch/x86/include/asm/hpet.h | 1 +
> arch/x86/kernel/hpet.c | 57 ++++++++++++++++++++++++++++---------
> 2 files changed, 45 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
> index f132fbf984d4..e7098740f5ee 100644
> --- a/arch/x86/include/asm/hpet.h
> +++ b/arch/x86/include/asm/hpet.h
> @@ -102,6 +102,7 @@ extern int hpet_rtc_timer_init(void);
> extern irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id);
> extern int hpet_register_irq_handler(rtc_irq_handler handler);
> extern void hpet_unregister_irq_handler(rtc_irq_handler handler);
> +extern void hpet_set_comparator(int num, unsigned int cmp, unsigned int period);
>
> #endif /* CONFIG_HPET_EMULATE_RTC */
>
> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> index 560fc28e1d13..c5c5fc150193 100644
> --- a/arch/x86/kernel/hpet.c
> +++ b/arch/x86/kernel/hpet.c
> @@ -289,6 +289,46 @@ static void hpet_legacy_clockevent_register(void)
> printk(KERN_DEBUG "hpet clockevent registered\n");
> }
>
> +/**
> + * hpet_set_comparator() - Helper function for setting comparator register
> + * @num: The timer ID
> + * @cmp: The value to be written to the comparator/accumulator
> + * @period: The value to be written to the period (0 = oneshot mode)
> + *
> + * Helper function for updating comparator, accumulator and period values.
> + *
> + * In periodic mode, HPET needs HPET_TN_SETVAL to be set before writing
> + * to the Tn_CMP to update the accumulator. Then, HPET needs a second
> + * write (with HPET_TN_SETVAL cleared) to Tn_CMP to set the period.
> + * The HPET_TN_SETVAL bit is automatically cleared after the first write.
> + *
> + * For one-shot mode, HPET_TN_SETVAL does not need to be set.
> + *
> + * See the following documents:
> + * - Intel IA-PC HPET (High Precision Event Timers) Specification
> + * - AMD-8111 HyperTransport I/O Hub Data Sheet, Publication # 24674
> + */
> +void hpet_set_comparator(int num, unsigned int cmp, unsigned int period)
> +{
> + if (period) {
> + unsigned int v = hpet_readl(HPET_Tn_CFG(num));
> +
> + hpet_writel(v | HPET_TN_SETVAL, HPET_Tn_CFG(num));
> + }
> +
> + hpet_writel(cmp, HPET_Tn_CMP(num));
> +
> + if (!period)
> + return;
> +
> + /* This delay is seldom used: never in one-shot mode and in periodic
> + * only when reprogramming the timer.
> + */

comment style warning ;)

> + udelay(1);
> + hpet_writel(period, HPET_Tn_CMP(num));
> +}
> +EXPORT_SYMBOL_GPL(hpet_set_comparator);
> +
> static int hpet_set_periodic(struct clock_event_device *evt, int timer)
> {
> unsigned int cfg, cmp, now;
> @@ -300,19 +340,10 @@ static int hpet_set_periodic(struct clock_event_device *evt, int timer)
> now = hpet_readl(HPET_COUNTER);
> cmp = now + (unsigned int)delta;
> cfg = hpet_readl(HPET_Tn_CFG(timer));
> - cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
> - HPET_TN_32BIT;
> - hpet_writel(cfg, HPET_Tn_CFG(timer));
> - hpet_writel(cmp, HPET_Tn_CMP(timer));
> - udelay(1);
> - /*
> - * HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL
> - * cleared) to T0_CMP to set the period. The HPET_TN_SETVAL
> - * bit is automatically cleared after the first write.
> - * (See AMD-8111 HyperTransport I/O Hub Data Sheet,
> - * Publication # 24674)
> - */
> - hpet_writel((unsigned int)delta, HPET_Tn_CMP(timer));
> + cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_32BIT;
> +
> + hpet_set_comparator(timer, cmp, (unsigned int)delta);
> +
> hpet_start_counter();
> hpet_print_config();
>
>


--
~Randy

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