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| author | Elias Vanderstuyft | 2015-10-14 17:29:37 -0700 |
|---|---|---|
| committer | Dmitry Torokhov | 2015-10-16 15:32:16 -0700 |
| commit | 33b96d934902f96e901b72ac18bbc47afad1ac20 (patch) | |
| tree | 5dcd2df3497f413de865e0f219905021effd49d7 /include/uapi | |
| parent | 52a9266788324edbbfd45f02cf23440c01ee0432 (diff) | |
Input: document and check on implicitly defined FF_MAX_EFFECTS
There is an undocumented upper bound for the total number of ff effects:
FF_GAIN (= 96).
This can be found as follows:
- user: write(EV_FF, effect_id, iterations)
calls kernel: ff->playback(effect_id, ...): starts effect "effect_id"
- user: write(EV_FF, FF_GAIN, gain)
calls kernel: ff->set_gain(gain, ...): sets gain
A collision occurs when effect_id equals FF_GAIN.
According to input_ff_event(),
FF_GAIN is the smallest value where a collision occurs.
Therefore the greatest safe value for effect_id is FF_GAIN - 1,
and thus the total number of effects should never exceed FF_GAIN.
Define FF_MAX_EFFECTS as FF_GAIN and check on this limit in ff-core.
Signed-off-by: Elias Vanderstuyft <elias.vds@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Diffstat (limited to 'include/uapi')
| -rw-r--r-- | include/uapi/linux/input.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h index a8e74b45dbe2..4f9f2a0f5573 100644 --- a/include/uapi/linux/input.h +++ b/include/uapi/linux/input.h @@ -414,6 +414,14 @@ struct ff_effect { #define FF_GAIN 0x60 #define FF_AUTOCENTER 0x61 +/* + * ff->playback(effect_id = FF_GAIN) is the first effect_id to + * cause a collision with another ff method, in this case ff->set_gain(). + * Therefore the greatest safe value for effect_id is FF_GAIN - 1, + * and thus the total number of effects should never exceed FF_GAIN. + */ +#define FF_MAX_EFFECTS FF_GAIN + #define FF_MAX 0x7f #define FF_CNT (FF_MAX+1) |