drm/i915: compute wait_ioctl timeout correctly

drm/i915: compute wait_ioctl timeout correctly

We've lost the +1 required for correct timeouts in

commit 5ed0bdf21a85d78e04f89f15ccf227562177cbd9
Author: Thomas Gleixner <[email protected]>
Date:   Wed Jul 16 21:05:06 2014 +0000

    drm: i915: Use nsec based interfaces

    Use ktime_get_raw_ns() and get rid of the back and forth timespec
    conversions.

    Signed-off-by: Thomas Gleixner <[email protected]>
    Acked-by: Daniel Vetter <[email protected]>
    Signed-off-by: John Stultz <[email protected]>
So fix this up by reinstating our handrolled _timeout function. While
at it bother with handling MAX_JIFFIES.

v2: Convert to usecs (we don't care about the accuracy anyway) first
to avoid overflow issues Dave Gordon spotted.

v3: Drop the explicit MAX_JIFFY_OFFSET check, usecs_to_jiffies should
take care of that already. It might be a bit too enthusiastic about it
though.

v4: Chris has a much nicer color, so use his implementation.

This requires to export nsec_to_jiffies from time.c.

Cc: Chris Wilson <[email protected]>
Cc: Dave Gordon <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82749
Cc: Thomas Gleixner <[email protected]>
Cc: John Stultz <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Acked-by: John Stultz <[email protected]>
Signed-off-by: Jani Nikula <[email protected]>