SPI: DUAL/QUAD support

[Thomas.Betker at rohde-schwarz.com]

Hello Mark:

> Well, there's two bits here.  One is the support in the client drivers
> for using the extra data lines and the other is the support in the SPI
> core for telling controllers to do this.  We need that second bit in
> place before the first one can be implemented.

I am not sure if we do. In the system I am working on, the QSPI controller 
recognizes the quad mode commands from the Tx data and automatically 
switches modes; no manual intervention by the flash driver is needed.

I agree that this may not be the case for all SPI controllers. Yuhang, can 
you tell us what your controller will do?

Best regards,
Thomas