linux-kernel - [PATCH 1/4] mfd: qnap-mcu: Calculate the checksum on the actual number of bytes received

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Message-ID: <20250923160853.1925674-2-heiko@sntech.de>
Date: Tue, 23 Sep 2025 18:08:50 +0200
From: Heiko Stuebner <heiko@...ech.de>
To: lee@...nel.org
Cc: linux-kernel@...r.kernel.org,
	heiko@...ech.de
Subject: [PATCH 1/4] mfd: qnap-mcu: Calculate the checksum on the actual number of bytes received

In the case of an error message, the number of received bytes can be
less than originally expected but still contain a valid message.

If the transfer itself ended in an error we would exit earlier already.

So calculate the checksum on the number of received bytes and not the
number of expected bytes.

Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
 drivers/mfd/qnap-mcu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/qnap-mcu.c b/drivers/mfd/qnap-mcu.c
index 2be429a50611..e3210541ec56 100644
--- a/drivers/mfd/qnap-mcu.c
+++ b/drivers/mfd/qnap-mcu.c
@@ -175,8 +175,8 @@ int qnap_mcu_exec(struct qnap_mcu *mcu,
 		return -ETIMEDOUT;
 	}
 
-	crc = qnap_mcu_csum(rx, reply_data_size);
-	if (crc != rx[reply_data_size]) {
+	crc = qnap_mcu_csum(rx, reply->received - QNAP_MCU_CHECKSUM_SIZE);
+	if (crc != rx[reply->received - QNAP_MCU_CHECKSUM_SIZE]) {
 		dev_err(&mcu->serdev->dev, "Invalid Checksum received\n");
 		return -EIO;
 	}
-- 
2.47.2