RE: [PATCH v2 1/3] Revert "mtd: spi-nor: remove Fujitsu MB85RS1MT support"

[Takahiro.Kuwano]

Hi Ronan,

> Hi Takahiro,
> 
> > We don't add any FRAM chips in SPI-NOR...
> 
> The SPI-NOR subsystem has support for the cy15x104q chips, which are
> FRAM chips. There is also support for Everspin MRAM chips, which are
> comparible to FRAM (and are also of small size).
> 
> Because of this, we thought there was precident to add support for this
> chip. I was under the impression that the opcodes used to interact with
> the chip had a greater significance than the underlying technology used,
> and this chip fits in with the other spi-nor chips based on that. Feel
> free to correct me if I'm wrong here.
> 
> > > The use is for a small amount of additional storage separate to the main
> > > system NAND flash for some small "critical" files that we don't want to
> > > lose. We've been using devices like the mchp23lcv1024 and mr25h40 on
> > > other products for some time.
> > >
> > For that use, how about using tmpfs with NVMEM backup?
> 
> Could you elaborate on this? I'm familiar with tmpfs but not with using
> NVMEM as a backup for it. Is there some method of syncing a tmpfs to
> NVMEM that the kernel provides?
> 
I didn't mean any kernel features, but we can dump tmpfs contents
from/to FRAM chip (exposed as NVMEM device) by 'dd'. Doesn't it meet
your system's requirement?

> Thanks,
> Ronan.