SPI: DUAL/QUAD support

[Gupta, Pekon]

> Just as Johannes said. In my patch m25p80's changes is incomplete.
> Because my inicial aim is to add the transfer width member to tell controller
> the mode flash in. And I will attach new patch about m25p80 later.
> Also you are right. There are really series of flashes do not support dual/quad
> transfer. So I don't know whether there are any standard for serial-flash just
> like the CFI for parallel-flash. Personally, to make a general standard and
> a general code for serial-flash is necessary. So that we do not need to add
> special function in m25p80.c.
> 
[Pekon]: Does below generic framework for spianand, suit your driver?
http://lists.infradead.org/pipermail/linux-mtd/2013-July/047434.html

you should be able to extend the generic spinand API for all
serial modes (SPI, Dual-SPI, Quad-SPI).
As QSPI and Dual-SPI devices should implicitly support SPI (MISO/MOSI)
So, you can do device probing using default SPI mode. And then based on
DT inputs and device support upgrade to QSPI / Dual-SPI mode.
And going forward extend it for direct memory-mapped device for XIP.


with regards, pekon