linux-kernel - Re: [PATCHv2 1/2] timekeeping: Provide new API to get the current time resolution

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Message-ID: <55245A9A.5070606@nod.at>
Date:	Wed, 08 Apr 2015 00:30:50 +0200
From:	Richard Weinberger <richard@....at>
To:	Harald Geyer <harald@...ib.org>,
	Jonathan Cameron <jic23@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 1/2] timekeeping: Provide new API to get the current
 time resolution

Am 07.04.2015 um 13:12 schrieb Harald Geyer:
> This patch series introduces a new function
> u32 ktime_get_resolution_ns(void)
> which allows to clean up some driver code.
> 
> In particular the IIO subsystem has a function to provide timestamps for
> events but no means to get their resolution. So currently the dht11 driver
> tries to guess the resolution in a rather messy and convoluted way. We
> can do much better with the new code.
> 
> This API is not designed to be exposed to user space.
> 
> This has been tested on i386, sunxi and mxs.
> 
> Signed-off-by: Harald Geyer <harald@...ib.org>
> ---
> changes since V1:
> Improved commit message.
> 
>  include/linux/timekeeping.h |    1 +
>  kernel/time/timekeeping.c   |   17 +++++++++++++++++
>  2 files changed, 18 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
> index 3eaae47..983b61e 100644
> --- a/include/linux/timekeeping.h
> +++ b/include/linux/timekeeping.h
> @@ -163,6 +163,7 @@ extern ktime_t ktime_get(void);
>  extern ktime_t ktime_get_with_offset(enum tk_offsets offs);
>  extern ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs);
>  extern ktime_t ktime_get_raw(void);
> +extern u32 ktime_get_resolution_ns(void);
>  
>  /**
>   * ktime_get_real - get the real (wall-) time in ktime_t format
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 91db941..8efd964 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -586,6 +586,23 @@ ktime_t ktime_get(void)
>  }
>  EXPORT_SYMBOL_GPL(ktime_get);
>  
> +u32 ktime_get_resolution_ns(void)
> +{
> +	struct timekeeper *tk = &tk_core.timekeeper;
> +	unsigned int seq;
> +	u32 nsecs;
> +
> +	WARN_ON(timekeeping_suspended);
> +
> +	do {
> +		seq = read_seqcount_begin(&tk_core.seq);
> +		nsecs = tk->tkr.mult >> tk->tkr.shift;
> +	} while (read_seqcount_retry(&tk_core.seq, seq));
> +
> +	return nsecs;
> +}
> +EXPORT_SYMBOL_GPL(ktime_get_resolution_ns);

Hmm, isn't this ktime_get_raw_ns()?

Thanks,
//richard
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