[U-Boot] SPI flash protection

[Albert ARIBAUD]

Le 30/01/2011 15:56, Simon Guinot a écrit :

>> So, if SPI Flash protection is possible on block or sector levels,
>> protect the blocks/sectors where U-Boot is located, including the
>> environment.
>
> For a Macronix SPI flash, the status register export 3 bits (or 4
> depending the model and size) to configure the block protection.
>
> Here is the protect area map for a MX25L4005A 4Mb flash:
>
>    bit  2 1 0 | protect level
>   ____________|_______________
>         0 0 0 | none
>         0 0 1 | block 7
>         0 1 0 | block 6-7
>         0 1 1 | block 4-7
>         1 * * | all
>
> As you can figure, deal with a per block protection in a generic way is
> not easy..

We don't necessarily have a generic per-block protection scheme at the 
HW level, but we can still use one as an API leve, i.e. have protect and 
unprotect functions which take generic start and end addresses and do 
what they can with the HW underneath (IIRC, protect on and protect off 
commands can use any address, and will check with the HW).

In your case, the HW seems to allow protecting 1, 2, 4 or all blocks 
from top of SPI Flash (I assume the boot process fetches code from a 
protectable areas, inside block 7 I imagine). I also assume you put 
U-Boot in the top blocks -- 7 alone, or 7 and 6 if too big for one 
block, etc.

Can the HW erase only one sector inside a block? If not, then you'd have 
to sacrifice a whole block for the env. Otherwise, you can lump together 
a sector for env and the sectors for U-Boot, hopefully in a single block.

>> Saveenv should unprotect and re-protect the environment sector/block.
>
> If I understand well, macronix_{erase,write}() are called from either
> "saveenv" or "spi erase/write" commands and the low level macronix
> functions don't have any flash map knowledge. Then, leave protect or not
> a flash sector after a write/erase operation is not an easy decision.
>
> Maybe the status register protection can be configured during the board
> initialization ? after all, the required flash informations (as device
> size, u-boot and environment localization) are available within the
> board setup code.

Can't the status register be re-programmed? Is it a kind of "protect now 
and until power-off" mechanism? If it is, then rewriting the environment 
will not be possible with this protection mechanism, and you might have 
to fake protection by software inside the driver if you need it. :(

> As a side note, the Macronix Linux driver (m25p80) don't deal either
> with the block protect bits.
>
>>
>>> Simon
>>>
>>> PS: some pointers about this project:
>>>
>>> git : http://git.lacie-nas.org/u-boot-lacie.git (branch netspace_v2)
>>
>> You should keep this branch based on u-boot/master generally, and on
>> u-boot-arm/master right now because it has the most recent ARM commits.
>
> OK, done :)

Fine. :)

> Simon

Amicalement,
-- 
Albert.