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 [email protected]

Fixes 0b813658c115 ("eeprom: at24: add support for at24mac series")

Signed-off-by Bartosz Golaszewski <[email protected]>

---
 drivers/misc/eeprom/at24.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

drivers/misc/eeprom/at24.c +4 -2

index e0b4b36ef010..72adf34627f5 100644
@@ -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

Am 27.11.2017 um 13:28 schrieb Bartosz Golaszewski:

Quoted 35 lines

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 [email protected]

Fixes 0b813658c115 ("eeprom: at24: add support for at24mac series")

Signed-off-by Bartosz Golaszewski <[email protected]>

---
 drivers/misc/eeprom/at24.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

drivers/misc/eeprom/at24.c +4 -2

index e0b4b36ef010..72adf34627f5 100644
@@ -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

drivers/misc/eeprom/at24.c static const struct i2c_device_id at24_ids[] = { · line 157

Quoted 10 lines

drivers/misc/eeprom/at24.c +7 -0

+      * 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 */

I'm afraid this won't work. byte_len = BIT(least 5 bits of magic value) Means byte_len for 24mac402 would be BIT(6) = 64 with your patch.

What we could do, although it seems to be quite ugly: round up the ilog2 value. Instead of ilog2(_len) we could use ilog2((_len) * 2 - 1)

Rgds, Heiner