linux-kernel - [PATCH 3/4] mfd: qnap-mcu: Move checksum verification to its own function

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Message-ID: <20250923160853.1925674-4-heiko@sntech.de>
Date: Tue, 23 Sep 2025 18:08:52 +0200
From: Heiko Stuebner <heiko@...ech.de>
To: lee@...nel.org
Cc: linux-kernel@...r.kernel.org,
	heiko@...ech.de
Subject: [PATCH 3/4] mfd: qnap-mcu: Move checksum verification to its own function

We'll need the checksum check in a second place in the future, so
move the verification code to a separate function.

Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
 drivers/mfd/qnap-mcu.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/mfd/qnap-mcu.c b/drivers/mfd/qnap-mcu.c
index b4b630f7d413..cd836bdd44a8 100644
--- a/drivers/mfd/qnap-mcu.c
+++ b/drivers/mfd/qnap-mcu.c
@@ -78,6 +78,13 @@ static u8 qnap_mcu_csum(const u8 *buf, size_t size)
 	return csum;
 }
 
+static bool qnap_mcu_verify_checksum(const u8 *buf, size_t size)
+{
+	u8 crc = qnap_mcu_csum(buf, size - QNAP_MCU_CHECKSUM_SIZE);
+
+	return crc == buf[size - QNAP_MCU_CHECKSUM_SIZE];
+}
+
 static int qnap_mcu_write(struct qnap_mcu *mcu, const u8 *data, u8 data_size)
 {
 	unsigned char tx[QNAP_MCU_TX_BUFFER_SIZE];
@@ -150,7 +157,6 @@ int qnap_mcu_exec(struct qnap_mcu *mcu,
 	size_t length = reply_data_size + QNAP_MCU_CHECKSUM_SIZE;
 	struct qnap_mcu_reply *reply = &mcu->reply;
 	int ret = 0;
-	u8 crc;
 
 	if (length > sizeof(rx)) {
 		dev_err(&mcu->serdev->dev, "expected data too big for receive buffer");
@@ -175,8 +181,7 @@ int qnap_mcu_exec(struct qnap_mcu *mcu,
 		return -ETIMEDOUT;
 	}
 
-	crc = qnap_mcu_csum(rx, reply->received - QNAP_MCU_CHECKSUM_SIZE);
-	if (crc != rx[reply->received - QNAP_MCU_CHECKSUM_SIZE]) {
+	if (!qnap_mcu_verify_checksum(rx, reply->received)) {
 		dev_err(&mcu->serdev->dev, "Invalid Checksum received\n");
 		return -EPROTO;
 	}
-- 
2.47.2