linux-kernel - Re: [PATCH v20 08/17] clocksource/drivers/arm_arch_timer: Rework counter frequency detection.

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Message-ID: <cafa8c7a-9c7c-51ba-5566-0cfe1fe6f764@linaro.org>
Date:   Thu, 19 Jan 2017 16:02:28 +0800
From:   Hanjun Guo <hanjun.guo@...aro.org>
To:     fu.wei@...aro.org, rjw@...ysocki.net, lenb@...nel.org,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        marc.zyngier@....com, mark.rutland@....com,
        lorenzo.pieralisi@....com, sudeep.holla@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linaro-acpi@...ts.linaro.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        rruigrok@...eaurora.org, harba@...eaurora.org, cov@...eaurora.org,
        timur@...eaurora.org, graeme.gregory@...aro.org,
        al.stone@...aro.org, jcm@...hat.com, wei@...hat.com, arnd@...db.de,
        catalin.marinas@....com, will.deacon@....com,
        Suravee.Suthikulpanit@....com, leo.duran@....com, wim@...ana.be,
        linux@...ck-us.net, linux-watchdog@...r.kernel.org,
        tn@...ihalf.com, christoffer.dall@...aro.org, julien.grall@....com
Subject: Re: [PATCH v20 08/17] clocksource/drivers/arm_arch_timer: Rework
 counter frequency detection.

Hi Fuwei,

One comments below.

On 2017/1/18 21:25, fu.wei@...aro.org wrote:
> From: Fu Wei <fu.wei@...aro.org>
>
> The counter frequency detection call(arch_timer_detect_rate) combines two
> ways to get counter frequency: system coprocessor register and MMIO timer.
> But in a specific timer init code, we only need one way to try:
> getting frequency from MMIO timer register will be needed only when we
> init MMIO timer; getting frequency from system coprocessor register will
> be needed only when we init arch timer.
>
> This patch separates paths to determine frequency:
> Separate out the MMIO frequency and the sysreg frequency detection call,
> and use the appropriate one for the counter.
>
> Signed-off-by: Fu Wei <fu.wei@...aro.org>
> ---
>  drivers/clocksource/arm_arch_timer.c | 40 ++++++++++++++++++++++--------------
>  1 file changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 6484f84..9482481 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -488,23 +488,33 @@ static int arch_timer_starting_cpu(unsigned int cpu)
>  	return 0;
>  }
>
> -static void arch_timer_detect_rate(void __iomem *cntbase)
> +static void __arch_timer_determine_rate(u32 rate)
>  {
> -	/* Who has more than one independent system counter? */
> -	if (arch_timer_rate)
> -		return;
> +	/* Check the timer frequency. */
> +	if (!arch_timer_rate) {
> +		if (rate)
> +			arch_timer_rate = rate;
> +		else
> +			pr_warn("frequency not available\n");
> +	} else if (rate && arch_timer_rate != rate) {
                         ^
Typo? I think it's "&" here.

Thanks
Hanjun