linux-kernel - Re: [PATCH] ALSA: es1968: Replace timeval with ktime

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Date:	Thu, 30 Oct 2014 08:06:10 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Tina Ruchandani <ruchandani.tina@...il.com>
Cc:	arnd@...db.de, perex@...ex.cz, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: es1968: Replace timeval with ktime_t

At Wed, 29 Oct 2014 10:48:10 -0700,
Tina Ruchandani wrote:
> 
> es1968_measure_clock uses struct timeval, which on 32-bit systems will overflow
> in 2038, leading to incorrect interpretation of time.This patch changes the
> function to use ktime_t instead of struct timeval, which implies:
> - no y2038: ktime_t uses a 64-bit datatype explicitly.
> - efficent subtraction: The earlier version computes the difference in usecs
>   while dealing with secs and nsecs. It requires checks to see if the nsecs of
>   stop is less than start. This patch uses a direct subtract of ktime_t and
>   converts to usecs.
> - use of monotonic clock (ktime_get) over real time (do_gettimeofday),
>   which simplifies timekeeping, as it does not have to deal with cases
>   where stop_time is less than start_time.
> 
> Signed-off-by: Tina Ruchandani <ruchandani.tina@...il.com>
> Reviewed-by: Arnd Bergmann <arnd@...db.de>

Applied, thanks.


Takashi

> ---
>  sound/pci/es1968.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/sound/pci/es1968.c b/sound/pci/es1968.c
> index a9956a7..6039700 100644
> --- a/sound/pci/es1968.c
> +++ b/sound/pci/es1968.c
> @@ -1710,7 +1710,8 @@ static void es1968_measure_clock(struct es1968 *chip)
>  	int i, apu;
>  	unsigned int pa, offset, t;
>  	struct esm_memory *memory;
> -	struct timeval start_time, stop_time;
> +	ktime_t start_time, stop_time;
> +	ktime_t diff;
>  
>  	if (chip->clock == 0)
>  		chip->clock = 48000; /* default clock value */
> @@ -1761,12 +1762,12 @@ static void es1968_measure_clock(struct es1968 *chip)
>  	snd_es1968_bob_inc(chip, ESM_BOB_FREQ);
>  	__apu_set_register(chip, apu, 5, pa & 0xffff);
>  	snd_es1968_trigger_apu(chip, apu, ESM_APU_16BITLINEAR);
> -	do_gettimeofday(&start_time);
> +	start_time = ktime_get();
>  	spin_unlock_irq(&chip->reg_lock);
>  	msleep(50);
>  	spin_lock_irq(&chip->reg_lock);
>  	offset = __apu_get_register(chip, apu, 5);
> -	do_gettimeofday(&stop_time);
> +	stop_time = ktime_get();
>  	snd_es1968_trigger_apu(chip, apu, 0); /* stop */
>  	snd_es1968_bob_dec(chip);
>  	chip->in_measurement = 0;
> @@ -1777,12 +1778,8 @@ static void es1968_measure_clock(struct es1968 *chip)
>  	offset &= 0xfffe;
>  	offset += chip->measure_count * (CLOCK_MEASURE_BUFSIZE/2);
>  
> -	t = stop_time.tv_sec - start_time.tv_sec;
> -	t *= 1000000;
> -	if (stop_time.tv_usec < start_time.tv_usec)
> -		t -= start_time.tv_usec - stop_time.tv_usec;
> -	else
> -		t += stop_time.tv_usec - start_time.tv_usec;
> +	diff = ktime_sub(stop_time, start_time);
> +	t = ktime_to_us(diff);
>  	if (t == 0) {
>  		dev_err(chip->card->dev, "?? calculation error..\n");
>  	} else {
> -- 
> 2.1.0.rc2.206.gedb03e5
> 
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