[flashrom] MX25L25635F with 4BA patch

[Boris Baykov]

> > > Alexander Amelkin wrote:
> > >
> > > Also, I couldn't manage to make this patch work with MXIC MX25L25635F
> > > chip which supports all the 4BA modes (direct, EN4B, EAR). I tried
> > > various combinations, but it couldn't properly erase the chip anyway.
> > > Didn't work in SFDP mode as well (only SFDP 1.0 is supported by the
> > > chip). Hence, I couldn't check if it reads back properly what was
> > > written. I didn't do any debugging though to find out the reason.
> > 
> > Try to to uncomment FBA_USE_EXT_ADDR_REG_BY_DEFAULT define
> > It may work after.
> > 
> I'll try that. Thanks.

By checking MX25L25635F datasheet I found that the Enter4BA instruction 
doesn't require WREN before. By default 4BA patch does WREN + Enter4BA
to switch to 4-byte.addr.mode.

To make Flashrom work with this chip I see 3 ways:

1) Uncomment FBA_USE_EXT_ADDR_REG_BY_DEFAULT define in sfdp.c to use 3-bytes
addressing with Extended Address Register by default. This should work on
MX25L25635F. It seems that it's the best way for default access to 4BA-chips.

2) Define this chip in flashchips.c with all direct functions (it has them)
or define with 4BA functions and set "enter_4ba = spi_enter_4ba_b7" to
prevent of using WREN before EN4B instruction.

3) Add some heuristics to 4BA mode switch to try both types
(with WREN and without WREN).