[meta-freescale] [PATCH 0/1] arm: imx: fsl_otp: make fuses (OTP memory) read-only

[Eric Bénard]

Hi Alexander,

Le Sun, 09 Nov 2014 11:14:39 +0100,
Alexander Holler <holler at ahsoftware.de> a écrit :

> Am 08.11.2014 19:49, schrieb Alexander Holler:
> 
> > I'm not confused, at least not in regard what you want to suggest. Of
> > course, I'm totally confused about the fact that almost nobody else
> > before has critized that write functionality of this driver, also I'm
> > already used to the fact that I'm unable to understand many things which
> > are happing in todays world. But nobody is perfect. ;)
> 
> Just to make it more clear what this thread is about, here is a relevant 
> sentence copied form the reference manual for the chip:
> 
> "In order to avoid "rogue" code performing erroneous writes to OTP, a 
> special unlocking sequence is required for writes to the fuse banks."
> 
That's why adding an unlock sysfs entry would match the required
sequence to unlock the write access on the user point of view, but
that's Freescale's problem and policy.

> Now guess why the HW was designed this way. And then look again at the 
> driver which nullifies the careful implementation in the HW. It doesn't 
> have to be the fault of the author, e.g. he just might have written it 
> for internal use. The problem is that it went into kernels for public 
> use and nobody has seen a problem. Might be because of missing knowledge 
> about what the driver does at all or whatever. I don't know.
> 
Evaluation boards come with unlocked/unburned fuse so if a designer
wants to evaluate his fuse configuration on an EVB during the design
phase of his custom product he may need this driver especially when
using Freescale's MFG Tools.
If your Wandboard has unburned fuses and their kernel has this driver,
then ask them why they keep this features open to their users by default
(this can be because the SOM are intended to be used in final products
and they let the final user of their SOM burn what he wants in the fuse
 - his own MAC address for example - so here again that's the job of the
end product designer to remove this feature once he launch his product
on the market).

Best regards,
Eric