linux-kernel - Re: [PATCH] Input: joystick: gf2k - change msleep to usleep

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Message-ID: <20161129065155.GD10549@suse.com>
Date:   Tue, 29 Nov 2016 07:51:55 +0100
From:   Vojtech Pavlik <vojtech@....cz>
To:     Aniroop Mathur <a.mathur@...sung.com>
Cc:     dmitry.torokhov@...il.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, s.samuel@...sung.com,
        r.mahale@...sung.com, aniroop.mathur@...il.com
Subject: Re: [PATCH] Input: joystick: gf2k - change msleep to usleep_range
 for small msecs

On Tue, Nov 29, 2016 at 01:11:49AM +0530, Aniroop Mathur wrote:

> msleep(1~20) may not do what the caller intends, and will often sleep longer.
> (~20 ms actual sleep for any value given in the 1~20ms range)
> This is not the desired behaviour for many cases like device resume time,
> device suspend time, device enable time, connection time, probe time,
> loops, retry logic, etc
> msleep is built on jiffies / legacy timers which are not precise whereas
> usleep_range is build on top of hrtimers so the wakeups are precise.
> Thus, change msleep to usleep_range for precise wakeups.
> 
> For example:
> On a machine with tick rate / HZ as 100, msleep(4) will make the process to
> sleep for a minimum period of 10 ms whereas usleep_range(4000, 4100) will make
> sure that the process does not sleep for more than 4100 us or 4.1ms

And once more, patch not needed.

> 
> Signed-off-by: Aniroop Mathur <a.mathur@...sung.com>
> ---
>  drivers/input/joystick/gf2k.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/input/joystick/gf2k.c b/drivers/input/joystick/gf2k.c
> index 0f519db..e9d5095 100644
> --- a/drivers/input/joystick/gf2k.c
> +++ b/drivers/input/joystick/gf2k.c
> @@ -42,7 +42,7 @@ MODULE_LICENSE("GPL");
>  
>  #define GF2K_START		400	/* The time we wait for the first bit [400 us] */
>  #define GF2K_STROBE		40	/* The time we wait for the first bit [40 us] */
> -#define GF2K_TIMEOUT		4	/* Wait for everything to settle [4 ms] */
> +#define GF2K_TIMEOUT		4000	/* Wait for everything to settle [4000 us] */
>  #define GF2K_LENGTH		80	/* Max number of triplets in a packet */
>  
>  /*
> @@ -138,7 +138,7 @@ static void gf2k_trigger_seq(struct gameport *gameport, short *seq)
>  	i = 0;
>          do {
>  		gameport_trigger(gameport);
> -		t = gameport_time(gameport, GF2K_TIMEOUT * 1000);
> +		t = gameport_time(gameport, GF2K_TIMEOUT);
>  		while ((gameport_read(gameport) & 1) && t) t--;
>                  udelay(seq[i]);
>          } while (seq[++i]);
> @@ -259,11 +259,11 @@ static int gf2k_connect(struct gameport *gameport, struct gameport_driver *drv)
>  
>  	gf2k_trigger_seq(gameport, gf2k_seq_reset);
>  
> -	msleep(GF2K_TIMEOUT);
> +	usleep_range(GF2K_TIMEOUT, GF2K_TIMEOUT + 100);
>  
>  	gf2k_trigger_seq(gameport, gf2k_seq_digital);
>  
> -	msleep(GF2K_TIMEOUT);
> +	usleep_range(GF2K_TIMEOUT, GF2K_TIMEOUT + 100);
>  
>  	if (gf2k_read_packet(gameport, GF2K_LENGTH, data) < 12) {
>  		err = -ENODEV;
> -- 
> 2.6.2
> 

-- 
Vojtech Pavlik