On 23/05/2016 at 14:53:15 +0200, Boris Brezillon wrote :

quoted

Well, I think we're reaching this point right now: I have to implement
"freeze" mode (entering a deep sleep mode by cutting all power domains
except VDDBU), and in order to do that I need to access BUREGs which
are part of the secu-sram you're trying to expose here.

Two comments on the nvmem approach:
1/ first of all it's not really a non-volative memory: if you loose
VDDBU you also loose the whole SRAM content.
2/ I need to be able to reserve the BUREG region (at least part of it)
for in kernel usage (need to store the SDRAM address I should jump to
when exiting freeze mode).

Forget this aspect. As Alexandre pointed out, the nvmem framework
provides an in-kernel API, so reserving space for the "freeze" mode
implementation is doable. But need to use the securam for advanced
stuff (like executing code from there) then the SRAM driver approach is
more future-proof IMO.

Yeah, in case we want to use the SRAM to actually run some code, we will
need the sram driver.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com