linux-kernel - [RFC PATCH 2/2] HID: usbhid: Don't include report ID zero into returned data

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Message-Id: <20221205210354.11846-3-andrew.smirnov@gmail.com>
Date:   Mon,  5 Dec 2022 13:03:54 -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 2/2] HID: usbhid: Don't include report ID zero into returned data

Report ID of zero is a special case for ID-less reports, which by
definition do not have report ID as a part of their payload. Not
returning an extra zero also matches hidraw documentation,
specifically:

      For devices which do not use numbered reports, set the first
      byte to 0.  The returned report buffer will contain the report
      number in the first byte, followed by the report data read from
      the device.  For devices which do not use numbered reports, the
      report data will begin at the first byte of the returned buffer.

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/usbhid/hid-core.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index be4c731aaa65..575f09003602 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -874,18 +874,8 @@ static int usbhid_get_raw_report(struct hid_device *hid,
 	struct usb_device *dev = hid_to_usb_dev(hid);
 	struct usb_interface *intf = usbhid->intf;
 	struct usb_host_interface *interface = intf->cur_altsetting;
-	int skipped_report_id = 0;
 	int ret;
 
-	/* Byte 0 is the report number. Report data starts at byte 1.*/
-	buf[0] = report_number;
-	if (report_number == 0x0) {
-		/* Offset the return buffer by 1, so that the report ID
-		   will remain in byte 0. */
-		buf++;
-		count--;
-		skipped_report_id = 1;
-	}
 	ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
 		HID_REQ_GET_REPORT,
 		USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
@@ -893,10 +883,6 @@ static int usbhid_get_raw_report(struct hid_device *hid,
 		interface->desc.bInterfaceNumber, buf, count,
 		USB_CTRL_SET_TIMEOUT);
 
-	/* count also the report id */
-	if (ret > 0 && skipped_report_id)
-		ret++;
-
 	return ret;
 }
 
-- 
2.34.1