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authorElias Vanderstuyft <elias.vds@gmail.com>2015-10-14 17:29:37 -0700
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2015-10-16 15:32:16 -0700
commit33b96d934902f96e901b72ac18bbc47afad1ac20 (patch)
tree5dcd2df3497f413de865e0f219905021effd49d7 /include
parent52a9266788324edbbfd45f02cf23440c01ee0432 (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')
-rw-r--r--include/uapi/linux/input.h8
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)