[PATCH 04/16] mtd: spi-nor: aspeed: Add read training

[Boris Brezillon]

On Fri, 11 Oct 2019 15:55:25 +0200
Cédric Le Goater <clg at kaod.org> wrote:

 
> > (how can you determine if timings are good when IO pins always
> > stay high). Don't we have a command that return non-ff/non-0 data while
> > still being predictable and immutable?   
> 
> Not that I know of on these controllers.

It's not really a controller thing, more a chip thing. The ideal
solution would be to have a loopback mode or an internal SRAM you can
write then read back, but AFAICT it doesn't exists. There's the SFDP
table as Vignesh mentioned, but we have the following problems:

1/ it might be too small (definitely < 16k)
2/ some NORs don't support SFDP (maybe not the ones we care about
   though)