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Sun, 08 Nov 2026 22:11:29 -0800 (PST) Received: from dtor-ws.sjc.corp.google.com ([2a00:79e0:2ebe:8:3588:b56:78bf:db5e]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-372661ede11sm12201192eec.21.2026.11.08.22.11.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Nov 2026 22:11:28 -0800 (PST) From: Dmitry Torokhov To: Jiri Kosina , Benjamin Tissoires , Gideon Heinz Cc: =?UTF-8?q?Filipe=20La=C3=ADns?= , Bastien Nocera , Hans de Goede , Edwin Velds , Stuart Hayhurst , Andrey Smirnov , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 13/18] HID: logitech-hidpp: store device serial as a byte array Date: Sun, 8 Nov 2026 22:10:57 -0800 Message-ID: <20261109061103.2887636-14-dmitry.torokhov@gmail.com> X-Mailer: git-send-email 2.56.0.506.g506a7eabc5-goog In-Reply-To: <20261109061103.2887636-1-dmitry.torokhov@gmail.com> References: <20261109061103.2887636-1-dmitry.torokhov@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Device serial numbers are read from 4-byte protocol payloads only to be formatted as raw byte sequences with %4phD. Storing them as u32 requires unaligned pointer casts and dereferences that depend on endian-neutral memory layout, and the FAP-based serial helper reads from the RAP union member instead of the matching FAP payload. Represent device serial numbers as 4-byte arrays, copy the payload bytes with a fixed serial length constant, and read the FAP device information response from the FAP payload directly. Signed-off-by: Dmitry Torokhov --- drivers/hid/hid-logitech-hidpp.c | 28 +++++++++++++--------------- 1 file changed, 13 insertions(+), 15 deletions(-) diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c index c4ebfc4d66fe..3a3baeb9fbb9 100644 --- a/drivers/hid/hid-logitech-hidpp.c +++ b/drivers/hid/hid-logitech-hidpp.c @@ -48,6 +48,7 @@ MODULE_PARM_DESC(disable_tap_to_click, #define HIDPP_REPORT_SHORT_LENGTH 7 #define HIDPP_REPORT_LONG_LENGTH 20 #define HIDPP_REPORT_VERY_LONG_MAX_LENGTH 64 +#define HIDPP_SERIAL_LENGTH 4 #define HIDPP_REPORT_SHORT_SUPPORTED BIT(0) #define HIDPP_REPORT_LONG_SUPPORTED BIT(1) @@ -889,7 +890,8 @@ static char *hidpp_unifying_get_name(struct hidpp_device *hidpp_dev) return name; } -static int hidpp_unifying_get_serial(struct hidpp_device *hidpp, u32 *serial) +static int hidpp_unifying_get_serial(struct hidpp_device *hidpp, + u8 serial[HIDPP_SERIAL_LENGTH]) { struct hidpp_report response; int ret; @@ -903,11 +905,7 @@ static int hidpp_unifying_get_serial(struct hidpp_device *hidpp, u32 *serial) if (ret) return ret; - /* - * We don't care about LE or BE, we will output it as a string - * with %4phD, so we need to keep the order. - */ - *serial = *((u32 *)&response.rap.params[1]); + memcpy(serial, &response.rap.params[1], HIDPP_SERIAL_LENGTH); return 0; } @@ -915,14 +913,14 @@ static int hidpp_unifying_init(struct hidpp_device *hidpp) { struct hid_device *hdev = hidpp->hid_dev; const char *name; - u32 serial; + u8 serial[HIDPP_SERIAL_LENGTH]; int ret; - ret = hidpp_unifying_get_serial(hidpp, &serial); + ret = hidpp_unifying_get_serial(hidpp, serial); if (ret) return ret; - snprintf(hdev->uniq, sizeof(hdev->uniq), "%4phD", &serial); + snprintf(hdev->uniq, sizeof(hdev->uniq), "%4phD", serial); dbg_hid("HID++ Unifying: Got serial: %s\n", hdev->uniq); name = hidpp_unifying_get_name(hidpp); @@ -1030,7 +1028,8 @@ static int hidpp_root_get_protocol_version(struct hidpp_device *hidpp) #define CMD_GET_DEVICE_INFO 0x00 -static int hidpp_get_serial(struct hidpp_device *hidpp, u32 *serial) +static int hidpp_get_serial(struct hidpp_device *hidpp, + u8 serial[HIDPP_SERIAL_LENGTH]) { struct hidpp_report response; u8 feature_index; @@ -1047,22 +1046,21 @@ static int hidpp_get_serial(struct hidpp_device *hidpp, u32 *serial) if (ret) return ret; - /* See hidpp_unifying_get_serial() */ - *serial = *((u32 *)&response.rap.params[1]); + memcpy(serial, &response.fap.params[1], HIDPP_SERIAL_LENGTH); return 0; } static int hidpp_serial_init(struct hidpp_device *hidpp) { struct hid_device *hdev = hidpp->hid_dev; - u32 serial; + u8 serial[HIDPP_SERIAL_LENGTH]; int ret; - ret = hidpp_get_serial(hidpp, &serial); + ret = hidpp_get_serial(hidpp, serial); if (ret) return ret; - snprintf(hdev->uniq, sizeof(hdev->uniq), "%4phD", &serial); + snprintf(hdev->uniq, sizeof(hdev->uniq), "%4phD", serial); dbg_hid("HID++ DeviceInformation: Got serial: %s\n", hdev->uniq); return 0; -- 2.56.0.506.g506a7eabc5-goog