[U-Boot] [PATCH 1/1] arm: mx5: Add fuse supply gate enable in fsl_iim

[Benoît Thébaudeau]

On Friday, December 13, 2013 1:52:19 AM, Benoît Thébaudeau wrote:
> Dear Sergey Alyoshin,
> 
> On Thursday, December 12, 2013 5:46:21 PM, Sergey Alyoshin wrote:
> > Enable fuse supply gate before fuse programming and disable after.
> > 
> > Signed-off-by: Sergey Alyoshin <alyoshin.s at gmail.com>
> > Tested-by: Sergey Alyoshin <alyoshin.s at gmail.com>
> 
> Have you also tested without this patch first too? On which SoC?
> 
> My tests had shown that this is not required on i.MX51. It's probably the
> same
> on i.MX53. I have not checked if i.MX25 and i.MX35 also have such a bit, but
> they also work fine as is. This is not even done by Freescale:
> http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/tree/drivers/char/mxc_iim.c?h=imx_3.0.35_4.1.0
> 
> In the Reference Manual, nothing says in the IIM / fuse chapters that this
> bit
> is needed for proper programming. It is just described in the CCM register
> map,
> and nothing refers to it. It is perhaps only useful for test purposes. I'd
> vote
> for letting this bit untouched if possible.
> 
> Fabio, do you have more information from Freescale about this bit?

Also note that the data sheets of the i.MX51 and i.MX53 both mention a dedicated
VDD_FUSE pin, with several notes saying that it should not be powered if
programming is not required in order to avoid inadvertently blowing fuses in
read mode. These notes would not be required if this bit gating this supply by
default really did exactly that. I think that it is rather an internal feature
for Freescale only, e.g. to blow Freescale bits like UID in die production.

Best regards,
Benoît