Re: [RFC PATCH v3 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes

[Randy Dunlap]

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@xxxxxxxxx>
> Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
> Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Philippe Ombredanne <pombredanne@xxxxxxxx>
> Cc: Kate Stewart <kstewart@xxxxxxxxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Originally-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
>  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