[U-Boot] SPI flash protection

[Simon Guinot <simon@sequanux.org>]

Hi Reinhard,

On Mon, Jan 31, 2011 at 08:17:36AM +0100, Reinhard Meyer wrote:
> Dear Albert ARIBAUD, Simon Guinot,
> >
> >>>>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
> >>Block size is 64KB. The compiled U-Boot image is about 220KB and
> >>environment is 4KB. So, 4 blocks are required for U-Boot.
> 
> I don't know your particular hardware, but is not u-boot (or the
> initial bootloader if there is any) fetched from the *beginning*
> of the flash?
> 
> If so, you would have to *hardware* protect the *entire* flash.

Yes you are right. Moreover the protected blocks (for a same register
value) _could_ be different on an another Macronix device.
For example, larger flash use 4 bits instead of 3 for block protection.

> 
> In this case, a *software* protection mechanism like for NOR flash
> would be a better choice.

Or no protection at all. After all, there is no such mechanism
implemented for u-boot and Linux...

Best regards,

Simon
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