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

[Cédric Le Goater]

On 11/10/2019 16:29, Boris Brezillon wrote:
> 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)


Yes. The approach we follow has good results, once the data is 
qualified as good enough for the training. 

We had some issues back in 2014 with some chips on early systems 
and I think we could reduce the amount of the data read and the 
number of loops now. 

Thanks,

C.