queue-6.19/mctp-i2c-initialise-event-handler-read-bytes.patch

From 316ab82fdc75a05811f26fc64c436aa69f863fa2 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Tue, 13 Jan 2026 17:01:16 +0800
Subject: mctp i2c: initialise event handler read bytes

From: Matt Johnston <matt@codeconstruct.com.au>

[ Upstream commit 2a14e91b6d76639dac70ea170f4384c1ee3cb48d ]

Set a 0xff value for i2c reads of an mctp-i2c device. Otherwise reads
will return "val" from the i2c bus driver. For i2c-aspeed and
i2c-npcm7xx that is a stack uninitialised u8.

Tested with "i2ctransfer -y 1 r10@0x34" where 0x34 is a mctp-i2c
instance, now it returns all 0xff.

Fixes: f5b8abf9fc3d ("mctp i2c: MCTP I2C binding driver")
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Link: https://patch.msgid.link/20260113-mctp-read-fix-v1-1-70c4b59c741c@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/mctp/mctp-i2c.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/mctp/mctp-i2c.c b/drivers/net/mctp/mctp-i2c.c
index ecda1cc36391c..8043b57bdf250 100644
--- a/drivers/net/mctp/mctp-i2c.c
+++ b/drivers/net/mctp/mctp-i2c.c
@@ -243,7 +243,10 @@ static int mctp_i2c_slave_cb(struct i2c_client *client,
 
 	switch (event) {
 	case I2C_SLAVE_READ_REQUESTED:
+	case I2C_SLAVE_READ_PROCESSED:
+		/* MCTP I2C transport only uses writes */
 		midev->rx_pos = 0;
+		*val = 0xff;
 		break;
 	case I2C_SLAVE_WRITE_RECEIVED:
 		if (midev->rx_pos < MCTP_I2C_BUFSZ) {
-- 
2.51.0