mtd layer: support of hybrid flash(W25M161AW) having both NOR and NAND flash

[Boris Brezillon]

+MTD maintainers.

On Thu, 4 Jan 2018 14:08:42 +0000
Prabhakar Kushwaha <prabhakar.kushwaha at nxp.com> wrote:

> Hi All,
> 
> Winbond has come up with special flash i.e.  W25M161AW. It consist of Serial NOR(Die #0) and Serial NAND(Die #1) flash. 
> Means both NOR, NAND flashes are placed in W25M161AW controlled by single chip-select. 
> 
> "Software Die Select (C2h)" command is being used to switch die or flash.

Why are they so mean to us?! :-)
 
>  
> It looks to be quite unique chip and wondering if any kind framework or work in progress available to handle it. 
> I know that SPI-NAND framework discussions is still in progress.

Well, nothing impossible to handle, we just need to declare 2 MTD
devices (one NAND and one NOR). This being said, it looks like we'll
need this spi-flash abstraction we have been talking about with Marek
and Cyrille to properly support these use cases: flash devices will be
exposed through different sub-layers (spi-nor or spi-nand), but we need
a common way to detect those spi-flash chips. I looked at a few SPI
NAND and SPI NOR chips, and from what I've seen so far they were quite
different (the opcodes and CMD+ADDR+DATA sequences were quite
different) so I thought we were safe to start with a completely
unconnected SPI NAND framework and merge some bits in a spi-flash layer
afterwards, but this chip proves me wrong :-/.