[PATCH] mtd: cfi_cmdset_0001 - fixup for PC28F512P33TFA

[Joakim Tjernlund]

Christoph Fritz <chf.fritz at googlemail.com> wrote on 2014/04/01 17:09:51:
> 
> Hi Joakim,
> 
>  thanks for your input, please see my further comments below.
> 
> On Tue, 2014-04-01 at 13:15 +0200, Joakim Tjernlund wrote:
> > > There has been complaints in the past with no erase suspend.
> > > You get delays considering that an erase takes c.a 1 sek so
> > > once you get into a state where GC is erasing lots of blocks and 
other
> > > progs wants read/write you will notice.
> 
> Yes it's not a fine solution, it's a quirk for a hardware with issues.
> But here for me it's better to get delays than having to suffer from
> flash errors.
> 
> > > > > The document mentions other ways to get around this problem, I 
> > suggest you 
> > > > > explore
> > > > > these first.
> > > > 
> > > > Already tried the “0xFF” dummy write cycle suggestion, should have
> > > > mentioned that.
> > > 
> > > OK, but one more workaround(the udelay part) is required, right?
> > 
> > There something odd with the patches in the mentioned doc.
> > 1) "Resolving ERASE SUSPEND Hangups" touches the same code as
> > 2) "ERASE SUSPEND Following ERASE RESUME"
> > 
> > 1) says to add write(0xff) and 2) adds a udelay
> > 
> > What should it be, both? in what order?
> > 
> > I suspect that any write(0xff) can be there unconditionally, provided 
that 
> > the cmd0001 spec allows it.
> > The delay could be a quirk default to 0
> 
> I already tried all sorts of combinations of various delays and 0xff
> writes, which can be used wasteful without impact. And yes, errors are
> happening less -- but are still happening (at for example -2°C starting
> udev or a filesys-bench program like bonnie++).

Amazing Micron still sells these defect chips

> 
> Sure, it's possible that I missed the holy right
> delay-0xff-quirk-combination to get this NOR flash reliable working for
> its specified temperature range. But until nobody has found it, I would
> prefer to stick to my posted quirk and just disable suspend erase.

Problem is, if you add that quirk no-one will be able to remove it later 
so we
better make sure there isn't a less intrusive solution.

hmm, have you checked you bus timing? Perhaps you need to relax it 
somewhat.

> 
> Maybe someone from Micron can help?

Yes, you should contact them.

 Thanks
         Jocke