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SubjectRe: [PATCH] eeprom: at24: fix the magic value for at24mac402
2017-11-27 20:15 GMT+01:00 Heiner Kallweit <hkallweit1@gmail.com>:
> Am 27.11.2017 um 13:28 schrieb Bartosz Golaszewski:
>> 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@vger.kernel.org
>> Fixes: 0b813658c115 ("eeprom: at24: add support for at24mac series")
>> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.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 */
>>
> 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

This is exactly why we should get rid of these magic values. ;) Thanks
for spotting that.

Another (slightly cleaner) solution that comes to mind is checking the
eeprom type in probe and adjusting byte_len manually.

Thanks,
Bartosz

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