linux-kernel - [RFC PATCH 1/2] HID: uhid: Don't send the report ID if it's zero

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Message-Id: <20221205210354.11846-2-andrew.smirnov@gmail.com>
Date:   Mon,  5 Dec 2022 13:03:53 -0800
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     linux-input@...r.kernel.org
Cc:     Andrey Smirnov <andrew.smirnov@...il.com>,
        David Rheinsberg <david.rheinsberg@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: [RFC PATCH 1/2] HID: uhid: Don't send the report ID if it's zero

Report ID of zero is a special case handling ID-less reports and in
that case we should omit report ID from the payload being sent to the
backend.

Without this change UHID_DEV_NUMBERED_{FEATURE,OUTPUT}_REPORTS doesn't
represent a semantical difference.

Cc: David Rheinsberg <david.rheinsberg@...il.com>
Cc: Jiri Kosina <jikos@...nel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc: linux-input@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-usb@...r.kernel.org
Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
---
 drivers/hid/uhid.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 2a918aeb0af1..7551120215e8 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -273,11 +273,11 @@ static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
 }
 
 static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
-			       const u8 *buf, size_t count, u8 rtype)
+			       u8 *buf, size_t count, u8 rtype)
 {
 	struct uhid_device *uhid = hid->driver_data;
 	struct uhid_event *ev;
-	int ret;
+	int ret, skipped_report_id = 0;
 
 	if (!READ_ONCE(uhid->running) || count > UHID_DATA_MAX)
 		return -EIO;
@@ -286,6 +286,15 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
 	if (!ev)
 		return -ENOMEM;
 
+	/* Byte 0 is the report number. Report data starts at byte 1.*/
+	buf[0] = rnum;
+	if (buf[0] == 0x0) {
+		/* Don't send the Report ID */
+		buf++;
+		count--;
+		skipped_report_id = 1;
+	}
+
 	ev->type = UHID_SET_REPORT;
 	ev->u.set_report.rnum = rnum;
 	ev->u.set_report.rtype = rtype;
@@ -306,7 +315,7 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
 	if (uhid->report_buf.u.set_report_reply.err)
 		ret = -EIO;
 	else
-		ret = count;
+		ret = count + skipped_report_id;
 
 unlock:
 	mutex_unlock(&uhid->report_lock);
-- 
2.34.1