linux-kernel - [PATCH] usbhid: Interpret 0 length ff effects as infinite (0xffff) length effects

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Message-ID: <20221001221657.gexisc2egjn3mpog@localhost.localdomain>
Date:   Sat, 1 Oct 2022 22:16:57 +0000
From:   Paul Dino Jones <paul@...cefreak18.xyz>
To:     jikos@...nel.org, anssi.hannula@...il.com
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: [PATCH] usbhid: Interpret 0 length ff effects as infinite (0xffff)
 length effects

Greetings,

I started using my Accuforce V2 sim wheel on Linux. I was getting no
response from racing simulators through wine, while native linux test
tools worked properly. It appears that many real-world applications will
send 0 as the replay length, which was resulting in the behavior I was
observing (nothing). The PID document does not explicitly state that 0
length effects should be interpreted as infinite, but it does mention
null effects being infinite effects.

This patch will interpret 0 length force feedback effects as 0xffff
(infinite) length effects, leaving other values for replay length
unchanged.

Signed-off-by: Paul Dino Jones <paul@...cefreak18.xyz>
---
 drivers/hid/usbhid/hid-pidff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/usbhid/hid-pidff.c b/drivers/hid/usbhid/hid-pidff.c
index 3b4ee21cd811..70653451c860 100644
--- a/drivers/hid/usbhid/hid-pidff.c
+++ b/drivers/hid/usbhid/hid-pidff.c
@@ -301,7 +301,7 @@ static void pidff_set_effect_report(struct pidff_device *pidff,
 		pidff->block_load[PID_EFFECT_BLOCK_INDEX].value[0];
 	pidff->set_effect_type->value[0] =
 		pidff->create_new_effect_type->value[0];
-	pidff->set_effect[PID_DURATION].value[0] = effect->replay.length;
+	pidff->set_effect[PID_DURATION].value[0] = effect->replay.length == 0 ? 0xffff : effect->replay.length;
 	pidff->set_effect[PID_TRIGGER_BUTTON].value[0] = effect->trigger.button;
 	pidff->set_effect[PID_TRIGGER_REPEAT_INT].value[0] =
 		effect->trigger.interval;
-- 
2.35.1