Re: [PATCH] Input: Add support for CLOCK_BOOTTIME

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Thu, Dec 18, 2014 at 03:03:26AM +0530, Aniroop Mathur wrote:
> Hello Mr. Torokhov,
> 
> On Wed, Dec 17, 2014 at 11:50 PM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> > Hi Aniroop,
> >
> > On Tue, Dec 16, 2014 at 10:26:34PM +0530, Aniroop Mathur wrote:
> >> This patch adds support for CLOCK_BOOTTIME for input event timestamp.
> >> CLOCK_BOOTTIME includes suspend time, so it would allow aplications
> >> to get correct time difference between two events even when system
> >> resumes from suspend state.
> >>
> >> Signed-off-by: Aniroop Mathur <a.mathur@samsung.com>
> >> ---
> >>  drivers/input/evdev.c | 33 +++++++++++++++++++++------------
> >>  1 file changed, 21 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> >> index de05545..7825794 100644
> >> --- a/drivers/input/evdev.c
> >> +++ b/drivers/input/evdev.c
> >> @@ -28,6 +28,13 @@
> >>  #include <linux/cdev.h>
> >>  #include "input-compat.h"
> >>
> >> +enum clock_type {
> >> +     REAL = 0,
> >> +     MONO,
> >> +     BOOT,
> >> +     CLK_MAX
> >> +};
> >> +
> >>  struct evdev {
> >>       int open;
> >>       struct input_handle handle;
> >> @@ -108,8 +115,9 @@ static void evdev_queue_syn_dropped(struct evdev_client *client)
> >>       struct input_event ev;
> >>       ktime_t time;
> >>
> >> -     time = (client->clkid == CLOCK_MONOTONIC) ?
> >> -             ktime_get() : ktime_get_real();
> >> +     time = (client->clkid == CLOCK_REALTIME) ?
> >> +             ktime_get_real() : (client->clkid == CLOCK_MONOTONIC) ?
> >> +             ktime_get() : ktime_get_boottime();
> >>
> 
> Is this okay ?
> To improve readabilty,
> how about adding a new funtion to get time depending upon clkid like below ?
> time = get_clk_time(client->clkid);
> 
> static ktime_t get_clk_time(int id)
> {
>         switch (id) {
> 
>         case CLOCK_REALTIME:     return ktime_get_real();
>         case CLOCK_MONOTONIC: return ktime_get();
>         case CLOCK_BOOTTIME:    return ktime_get_bootime();
>         }
> }

Just open-code it in evdev_queue_syn_dropped() since there is only place
where we call it. And use clk_type instead of clock id-.

> 
> >>       ev.time = ktime_to_timeval(time);
> >>       ev.type = EV_SYN;
> >> @@ -159,7 +167,7 @@ static void __pass_event(struct evdev_client *client,
> >>
> >>  static void evdev_pass_values(struct evdev_client *client,
> >>                       const struct input_value *vals, unsigned int count,
> >> -                     ktime_t mono, ktime_t real)
> >> +                     ktime_t *ev_time)
> >>  {
> >>       struct evdev *evdev = client->evdev;
> >>       const struct input_value *v;
> >> @@ -169,8 +177,9 @@ static void evdev_pass_values(struct evdev_client *client,
> >>       if (client->revoked)
> >>               return;
> >>
> >> -     event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ?
> >> -                                   mono : real);
> >> +     event.time = ktime_to_timeval(client->clkid == CLOCK_REALTIME ?
> >> +                     ev_time[REAL] : client->clkid == CLOCK_MONOTONIC ?
> >> +                     ev_time[MONO] : ev_time[BOOT]);
> >
> > This becomes unwieldy. Should we have client->clk_type instead of
> > client->clkid and convert CLOCK_* into your EVDEV_CLK_{REAL|MONO|BOOT}
> > when setting it in ioctl and then do
> >
> >         event.time = ktime_to_timeval(ev_time[client->clk_offset]);
> >
> 
> Sure, using clk_type would be better and improve code readability.
> 
> I am afraid how converting CLOCK_* into your
> EVDEV_CLK_{REAL|MONO|BOOT} will help
> because we cannot have ev_time array size more than CLK_MAX (3).
> 
> Did you mean to have following changes:
> 
> 1. Add clk_type variable
> struct evdev_client {
>          int clkid:
>       + int clk_type;
> }

I meant replacing clkid with clk_type in evdev_client.

> 
> 2. Add new funtion for setting clk_type to improve readability
> static int set_clk_type(struct evdev_client *client, int id)


evdev_set_clk_type() to keep with the style.

> {
>         switch (id) {
> 
>         case CLOCK_REALTIME:     client->clk_type = EV_REAL;  break;
>         case CLOCK_MONOTONIC: client->clk_type = EV_MONO; break;
>         case CLOCK_BOOTTIME:    client->clk_type = EV_BOOT;  break;
>         default: return -1

-EINVAL here, otherwise yes.

>         }
> 
>         return 0;
> }
> 
> 3. Addition in ioctl call
>     case EVIOCSCLOCKID:
>     ...
>     if (!set_clk_type())
>            return -EINVAL;
> 

	error = evdev_set_clktype(i);
	if (error)
		return error;

>      client->clkid = i;

Drop this.

>      return 0;
> 
> 4. Change in evdev_pass_values function
> event.time = ktime_to_timeval(ev_time[client->clk_type]);

Yes.

> 
> >>
> >>       /* Interrupts are disabled, just acquire the lock. */
> >>       spin_lock(&client->buffer_lock);
> >> @@ -198,21 +207,21 @@ static void evdev_events(struct input_handle *handle,
> >>  {
> >>       struct evdev *evdev = handle->private;
> >>       struct evdev_client *client;
> >> -     ktime_t time_mono, time_real;
> >> +     ktime_t ev_time[CLK_MAX];
> >>
> >> -     time_mono = ktime_get();
> >> -     time_real = ktime_mono_to_real(time_mono);
> >> +     ev_time[MONO] = ktime_get();
> >> +     ev_time[REAL] = ktime_mono_to_real(ev_time[MONO]);
> >> +     ev_time[BOOT] = ktime_get_boottime();
> >
> > I do not think we want to use ktime_get_boottime() here; I'd rather you
> > use ktime_mono_to_anY(ev_time[MONO], TK_OFFS_BOOT) so that all 3 times
> > are consistent.
> >
> 
> Sure. I will send the updated patch with this change.
> 
> >>
> >>       rcu_read_lock();
> >>
> >>       client = rcu_dereference(evdev->grab);
> >>
> >>       if (client)
> >> -             evdev_pass_values(client, vals, count, time_mono, time_real);
> >> +             evdev_pass_values(client, vals, count, ev_time);
> >>       else
> >>               list_for_each_entry_rcu(client, &evdev->client_list, node)
> >> -                     evdev_pass_values(client, vals, count,
> >> -                                       time_mono, time_real);
> >> +                     evdev_pass_values(client, vals, count, ev_time);
> >>
> >>       rcu_read_unlock();
> >>  }
> >> @@ -874,7 +883,7 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
> >>       case EVIOCSCLOCKID:
> >>               if (copy_from_user(&i, p, sizeof(unsigned int)))
> >>                       return -EFAULT;
> >> -             if (i != CLOCK_MONOTONIC && i != CLOCK_REALTIME)
> >> +             if (i != CLOCK_MONOTONIC && i != CLOCK_REALTIME && i != CLOCK_BOOTTIME)
> >>                       return -EINVAL;
> >>               client->clkid = i;
> >>               return 0;
> >> --
> >> 1.9.1
> >>
> >
> > Thanks.
> >
> > --
> > Dmitry
> 
> Thanks,
> Aniroop Mathur

-- 
Dmitry