Re: [patch 0/5] Add MMC password protection (lock/unlock) support

[Anderson Lizardo]

On 12/29/05, Russell King <rmk+lkml@xxxxxxxxxxxxxxxx> wrote:
> On Thu, Dec 29, 2005 at 03:06:15PM -0400, Anderson Lizardo wrote:
> > On 12/15/05, Russell King <rmk+lkml@xxxxxxxxxxxxxxxx> wrote:
> > > Reading through the specs I have here, block sizes seem to be all over
> > > the place.  The MMC card specs seem to imply that any block size can
> > > be set, from 0 bytes to 2^32-1 bytes.
> > >
> > > The PXA MMC interface specification allows the block size to be anything
> > > from 1 to 1023 bytes, excluding CRC.  It is unclear whether a value of 0
> > > means 1024.
> > >
> > > The MMCI specification allows the block size to be specified as a power
> > > of two, from 1 to 2048 bytes, excluding CRC.
> >
> > By "allows" do you mean we can set the block size to arbitrary values
> > on MMCI too?
>
> No - that's not what I said.  I said "power of two, from 1 to 2048
> bytes excluding CRC."

Ah, so you meant "only allows", sorry for the confusion.

> > The MMC specification v4.1 is clear in one thing: the SET_BLOCKLEN
> > command should be issued prior to the actual LOCK_UNLOCK command with
> > *exactly* the password length + 2 bytes (which contains the operation
> > mode bits and the password length in bytes). The MMC password
> > unlocking (and other password operations, FWIW) doesn't work on the
> > OMAP host if the SET_BLOCKLEN command argument and the block size of
> > the data transfer itself do not match.
>
> Since passwords are limited to a maximum of 16 characters, this means
> that only passwords of length 2, 6, and 14 are possible with MMCI.
> All other passwords are invalid and/or impossible with this host.

What do you suggest in this case? So far the MMCI host seems the only
one (from those supported by mainline tree) that has such limitation.

--
Anderson Lizardo
Embedded Linux Lab - 10LE
Nokia Institute of Technology - INdT
Manaus - Brazil
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