[U-Boot] a few questions about saving bootcount in the environment

[Robert P. J. Day]

On Mon, 25 Jul 2016, Wolfgang Denk wrote:

> Dear Tom,
>
> In message <20160725135754.GN14698 at bill-the-cat> you wrote:
> >
> > > Right, it is only a last resort when you cannot find any better place
> > > to storeit (in a hardware register that survives resets).
> >
> > That's not strictly true.  One of the things I noticed recently is that
> > Mender uses bootcount, in environment, as a least common denominator.
> > And thrown in a file in a filesystem, in so far as you trust the
> > underlying black box to be good about reads/writes and wear levelling,
> > it's robust enough (for certain values of robust and enough).  We're
> > dipping into one of those areas where experts have varying opinions on
> > what's good enough, hence all the qualifiers.  But it is a useful
> > option.  And neatly circumvents the need for a "driver" to clear the
> > count too.
>
> Agreed.  Let me rephrase the warning, then: it is always a good idea
> to minimize the number of writes to the environment, especially when
> done automagically.  One should at least avoid to re-write it on every
> boot, especially when storage is some (flash based) storage device
> with a limited number of erase/write cycles.  And even on other stoage
> each write access includes the risk of errors.

  i'm sure i'm asking the obvious, but if every boot to user space is
successful, bootcount will have a value of zero each time, yes? so if
user space code checks it and it's zero, then, you're done, no need to
write.

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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