Date:   Tue, 29 Nov 2016 07:59:03 +0100
From:   "vojtech@....cz" <vojtech@....cz>
To:     Aniroop Mathur <a.mathur@...sung.com>
Cc:     "dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        SAMUEL SEQUEIRA <s.samuel@...sung.com>,
        Rahul Mahale <r.mahale@...sung.com>,
        "aniroop.mathur@...il.com" <aniroop.mathur@...il.com>
Subject: Re: Re: [PATCH] Input: joystick: adi - change msleep to usleep_range
 for small msecs

On Mon, Nov 28, 2016 at 01:49:31PM +0000, Aniroop Mathur wrote:
> Hello Mr. Vojtech Pavlik,
> 
> On 28 Nov 2016 17:23, "vojtech@....cz" <vojtech@....cz> wrote:
>  >
>  > Hi.
>  >
>  > ADI_INIT_DELAY/ADI_DATA_DELAY doesn't have to be exact, and a longer
>  > sleep doesn't matter. In the initilization sequence - first chunk of
>  > your patch - a way too long delay could in theory make the device fail
>  > to initialize. What's critical is that the mdelay() calls are precise.
>  >
>  > One day I'll open my box of old joystick and re-test these drivers to
>  > see if they survived the years of kernel infrastructure updates ...
>  >
>  > Vojtech
>  >
>  
>  Well, it seems to me that there is some kind of confusion, so I'd like to
>  clarify things about this patch.
>  As you have mentioned that in the initialization sequence, long delay could
>  in theory make the device fail to initialize - This patch actually solves
>  this problem.
>  msleep is built on jiffies / legacy timers and usleep_range is built on top
>  of hrtimers so the wakeup will be precise.
>  Source - https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
>  For example in initialization sequence, if we use msleep(4), then the process
>  could sleep for much more than 4 ms, say 6 ms or 10 ms or more depending on
>  machine architecture. Like on a machine with tick rate / HZ is defined to be
>  100 so msleep(4) will make the process to sleep for minimum 10 ms. 
>  Whereas usleep_range(4000, 4100) will make sure that the process do not sleep
>  for more than 4100 us or 4.1 ms. So usleep_range is precise but msleep is not.
>  
>  Originally, I added you in this patch to request you if you could help to
>  test this patch or provide contact points of individuals who could help
>  to test this patch as we do not have the hardware available with us?
>  Like this driver, we also need to test other joystick drivers as well like
>  gf2k.c, analog.c, sidewinder.c and gameport driver ns558.c as all have
>  similar problem.
>  Original patch link - https://patchwork.kernel.org/patch/9446201/
>  As we do not have hardware available, so we decided to split patch into
>  individual drivers and request to person who could support to test this patch
> 
>  I have also applied the same patch in our driver whose hardware is available
>  with me and I found that wake up time became precise indeed and so I
>  decided to apply the same fix in other input subsystem drivers as well.

I do understand what you're trying to achieve. Both ADI_DATA_DELAY and
ADI_INIT_DELAY are specified as minimum delays. Waiting longer doesn't
cause any trouble, so the patch doesn't need to change that.

In the initialization sequence, it probably doesn't matter either
whether we wait longer, hence the distinction between msleep() and
mdelay() based on positive/negative numbers. The mdelay() needs to be
exact and the msleep() can be longer. How much longer before it disturbs
the init sequence I'm not sure, probably quite a bit.

The driver was written a long time before hrtimers existed and as such
it was written expecting that msleep() can take a longer time.

So your patch is most likely not needed, but I should find an ADI device
and see what happens if I make the sleeps in the init sequence much
longer.

It'd also be interesting to see if the mdelay()s could be replaced with
hrtimer-based delays instead, as that would be nicer to the system - if
they can be precise enough. Also, preemption and maybe interrupts should
be disabled around the mdelays I suppose - that was not an issue when
the drivers were written.

Vojtech

>  
>  Thank you!
>  
>  BR,
>  Aniroop Mathur
> 
>  > On Mon, Nov 28, 2016 at 11:43:56AM +0000, 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, data reading time, etc.
>  > > Thus, change msleep to usleep_range for precise wakeups.
>  > >
>  > > Signed-off-by: Aniroop Mathur <a.mathur@...sung.com>
>  > > ---
>  > >  joystick/adi.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
>  > >
>  > > diff --git a/joystick/adi.c b/joystick/adi.c
>  > > index d09cefa..6799bd9 100644
>  > > --- a/joystick/adi.c
>  > > +++ b/joystick/adi.c
>  > > @@ -47,8 +47,8 @@ MODULE_LICENSE("GPL");
>  > >
>  > >  #define ADI_MAX_START                200     /* Trigger to packet timeout [200us] */
>  > >  #define ADI_MAX_STROBE               40      /* Single bit timeout [40us] */
>  > > -#define ADI_INIT_DELAY               10      /* Delay after init packet [10ms] */
>  > > -#define ADI_DATA_DELAY               4       /* Delay after data packet [4ms] */
>  > > +#define ADI_INIT_DELAY               10000   /* Delay after init packet [10ms] */
>  > > +#define ADI_DATA_DELAY               4000    /* Delay after data packet [4000us] */
>  > >
>  > >  #define ADI_MAX_LENGTH               256
>  > >  #define ADI_MIN_LENGTH               8
>  > > @@ -319,7 +319,7 @@ static void adi_init_digital(struct gameport *gameport)
>  > >       for (i = 0; seq[i]; i++) {
>  > >               gameport_trigger(gameport);
>  > >               if (seq[i] > 0)
>  > > -                     msleep(seq[i]);
>  > > +                     usleep_range(seq[i] * 1000, (seq[i] * 1000) + 100);
>  > >               if (seq[i] < 0) {
>  > >                       mdelay(-seq[i]);
>  > >                       udelay(-seq[i]*14);     /* It looks like mdelay() is off by approx 1.4% */
>  > > @@ -512,9 +512,9 @@ static int adi_connect(struct gameport *gameport, struct gameport_driver *drv)
>  > >       gameport_set_poll_handler(gameport, adi_poll);
>  > >       gameport_set_poll_interval(gameport, 20);
>  > >
>  > > -     msleep(ADI_INIT_DELAY);
>  > > +     usleep_range(ADI_INIT_DELAY, ADI_INIT_DELAY + 100);
>  > >       if (adi_read(port)) {
>  > > -             msleep(ADI_DATA_DELAY);
>  > > +             usleep_range(ADI_DATA_DELAY, ADI_DATA_DELAY + 100);
>  > >               adi_read(port);
>  > >       }
>  > >
>  > > --
>  > > 2.6.4.windows.1
>  >
>  >
>  > --
>  > Vojtech Pavlik


-- 
Vojtech Pavlik

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