linux-kernel - [PATCH] eeprom: at24: fix the magic value for at24mac402

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Date:   Mon, 27 Nov 2017 13:28:08 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        Claudiu Beznea <Claudiu.Beznea@...rochip.com>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <brgl@...ev.pl>, stable@...r.kernel.org
Subject: [PATCH] eeprom: at24: fix the magic value for at24mac402

There's an ilog2() expansion in AT24_DEVICE_MAGIC() which rounds down
the actual size of EUI-48 byte array in at24mac402 eeproms to 4 from 6,
making it impossible to read it all.

Fix it by creating the magic value manually with the correct size.

This patch contains a temporary fix that is suitable for stable
branches. Eventually we'll probably remove the call to ilog2() while
converting the magic values to actual structs.

This fix will cause a warning message to be emitted by probe() for
at24mac402 chips but theys should be initialized correctly anyway.

Cc: stable@...r.kernel.org
Fixes: 0b813658c115 ("eeprom: at24: add support for at24mac series")
Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
---
 drivers/misc/eeprom/at24.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index e0b4b36ef010..72adf34627f5 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -141,8 +141,17 @@ static const struct i2c_device_id at24_ids[] = {
 	{ "24c02",	AT24_DEVICE_MAGIC(2048 / 8,	0) },
 	{ "24cs02",	AT24_DEVICE_MAGIC(16,
 				AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
-	{ "24mac402",	AT24_DEVICE_MAGIC(48 / 8,
-				AT24_FLAG_MAC | AT24_FLAG_READONLY) },
+	/*
+	 * REVISIT: the size of the EUI-48 byte array is 6 in at24mac402, while
+	 * the call to ilog2() in AT24_DEVICE_MAGIC() rounds it down to 4. We
+	 * might want to eventually remove it altogether or maybe even convert
+	 * the magic values to real structs.
+	 *
+	 * For now just create the magic value manually with the right size.
+	 */
+	{ "24mac402",	((1 << AT24_SIZE_FLAGS |
+			 (AT24_FLAG_MAC | AT24_FLAG_READONLY))
+			 << AT24_SIZE_BYTELEN | (48 / 8)) },
 	{ "24mac602",	AT24_DEVICE_MAGIC(64 / 8,
 				AT24_FLAG_MAC | AT24_FLAG_READONLY) },
 	/* spd is a 24c02 in memory DIMMs */
-- 
2.15.0