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

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

[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 */
-- 
2.15.0

Re: [PATCH] eeprom: at24: fix the magic value for at24mac402

[Heiner Kallweit]

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

Re: [PATCH] eeprom: at24: fix the magic value for at24mac402

[Bartosz Golaszewski]

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