[PATCH] HID: gpd: fix report descriptor on GPD Win handheld (2f24:0137)

[honjow <honjow311@gmail.com>]

The OEM USB HID interface found on GPD Win handhelds (VID 2f24, registered
to ShenZhen HuiJiaZhi / GameSir, PID 0137) declares 63-byte Input and
Feature reports for Report ID 1, but the firmware only transfers 11 data
bytes per interrupt.

Since commit 0a3fe972a7cb ("HID: core: Mitigate potential OOB by removing
bogus memset()"), the HID core rejects undersized reports instead of zero-
padding them. This breaks the device entirely on kernels >= v7.0-rc5.

Fix it by patching the report descriptor in report_fixup(), reducing
Report Count from 63 to 11 for both Input and Feature.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221271
Signed-off-by: honjow <honjow311@gmail.com>
---
 drivers/hid/Kconfig   | 10 +++++++++
 drivers/hid/Makefile  |  1 +
 drivers/hid/hid-gpd.c | 52 +++++++++++++++++++++++++++++++++++++++++++
 drivers/hid/hid-ids.h |  3 +++
 4 files changed, 66 insertions(+)
 create mode 100644 drivers/hid/hid-gpd.c

diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index 10c12d8e65579..20c60f5aca4c5 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -419,6 +419,16 @@ config HID_GLORIOUS
 	  Support for Glorious PC Gaming Race mice such as
 	  the Glorious Model O, O- and D.
 
+config HID_GPD
+	tristate "GPD Win handheld OEM HID support"
+	depends on USB_HID
+	help
+	  Report descriptor fix for the OEM USB HID interface (GameSir
+	  2f24:0137) found on GPD Win handhelds. The firmware declares 63-byte
+	  reports but only sends 11 bytes, which the HID core rejects.
+
+	  Say Y or M here if you use a GPD Win handheld with this interface.
+
 config HID_HOLTEK
 	tristate "Holtek HID devices"
 	depends on USB_HID
diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
index 07dfdb6a49c59..03ef72ec4499f 100644
--- a/drivers/hid/Makefile
+++ b/drivers/hid/Makefile
@@ -53,6 +53,7 @@ obj-$(CONFIG_HID_ELO)		+= hid-elo.o
 obj-$(CONFIG_HID_EVISION)	+= hid-evision.o
 obj-$(CONFIG_HID_EZKEY)		+= hid-ezkey.o
 obj-$(CONFIG_HID_FT260)		+= hid-ft260.o
+obj-$(CONFIG_HID_GPD)		+= hid-gpd.o
 obj-$(CONFIG_HID_GEMBIRD)	+= hid-gembird.o
 obj-$(CONFIG_HID_GFRM)		+= hid-gfrm.o
 obj-$(CONFIG_HID_GLORIOUS)  += hid-glorious.o
diff --git a/drivers/hid/hid-gpd.c b/drivers/hid/hid-gpd.c
new file mode 100644
index 0000000000000..5b4d203e24995
--- /dev/null
+++ b/drivers/hid/hid-gpd.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID report descriptor fixup for GPD Win handhelds.
+ *
+ *  The OEM HID interface (VID 2f24 / GameSir, PID 0137) declares Report ID 1
+ *  with Report Count 63 (8-bit fields) for both Input and Feature, but the
+ *  firmware only sends 11 bytes of payload after the report ID.
+ */
+
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+#define RDESC_LEN		38
+#define RPT_COUNT_INPUT_OFF	21
+#define RPT_COUNT_FEATURE_OFF	34
+
+static const __u8 *gpd_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+				    unsigned int *rsize)
+{
+	if (*rsize != RDESC_LEN)
+		return rdesc;
+
+	if (rdesc[RPT_COUNT_INPUT_OFF - 1] == 0x95 &&
+	    rdesc[RPT_COUNT_INPUT_OFF] == 0x3f &&
+	    rdesc[RPT_COUNT_FEATURE_OFF - 1] == 0x95 &&
+	    rdesc[RPT_COUNT_FEATURE_OFF] == 0x3f) {
+		hid_info(hdev, "fixing report counts (63 -> 11 bytes)\n");
+		rdesc[RPT_COUNT_INPUT_OFF] = 11;
+		rdesc[RPT_COUNT_FEATURE_OFF] = 11;
+	}
+
+	return rdesc;
+}
+
+static const struct hid_device_id gpd_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_GAMESIR, USB_DEVICE_ID_GAMESIR_0137) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, gpd_devices);
+
+static struct hid_driver gpd_driver = {
+	.name = "gpd",
+	.id_table = gpd_devices,
+	.report_fixup = gpd_report_fixup,
+};
+
+module_hid_driver(gpd_driver);
+
+MODULE_DESCRIPTION("HID report descriptor fix for GPD Win handheld (GameSir 2f24:0137)");
+MODULE_LICENSE("GPL");
diff --git a/drivers/hid/hid-ids.h b/drivers/hid/hid-ids.h
index 933b7943bdb50..d0a6c19baa660 100644
--- a/drivers/hid/hid-ids.h
+++ b/drivers/hid/hid-ids.h
@@ -533,6 +533,9 @@
 #define USB_VENDOR_ID_FRUCTEL	0x25B6
 #define USB_DEVICE_ID_GAMETEL_MT_MODE	0x0002
 
+#define USB_VENDOR_ID_GAMESIR		0x2f24
+#define USB_DEVICE_ID_GAMESIR_0137	0x0137
+
 #define USB_VENDOR_ID_GAMEVICE	0x27F8
 #define USB_DEVICE_ID_GAMEVICE_GV186	0x0BBE
 #define USB_DEVICE_ID_GAMEVICE_KISHI	0x0BBF
-- 
2.51.2