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

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