[RFC PATCH 0/2] spi: add dual parallel & stacked mode support in Zynq MPSoC GQSPI controller

[Ranjit Abhimanyu Waghmode]

Hi Mark,

> > What is dual parallel mode?
> > ---------------------------
> > ZynqMP GQSPI controller supports Dual Parallel mode with following
> functionalities:
> > 1) Supporting two SPI flash memories operating in parallel. 8 I/O lines.
> > 2) Chip selects and clock are shared to both the flash devices
> > 3) This mode is targeted for faster read/write speed and also doubles the size
> > 4) Commands/data can be transmitted/received from both the devices(mirror),
> >    or only upper or only lower flash memory devices.
> > 5) Data arrangement:
> >    With stripe enabled,
> >    Even bytes i.e. 0, 2, 4,... are transmitted on Lower Data Bus
> >    Odd bytes i.e. 1, 3, 5,.. are transmitted on Upper Data Bus.
> 
> For the SPI code this just seems like SPI with an 8 bit data width.
> 
> > What is stacked mode?
> > ---------------------
> > ZynqMP GQSPI controller supports stacked mode with following
> functionalities:
> > 1) The Generic Quad-SPI controller also supports two SPI flash memories
> >    in a shared bus arrangement to reduce IO pin count.
> > 2) Separate chip select lines
> > 3) Shared I/O lines
> > 4) This mode is targeted for increasing the flash memory and no performance
> >    improvement when compared with single.
> 
> This is just a normal SPI controller from a SPI point of view.

How can we really represent the stacked mode in current configuration?

Thanks & Regards,
Ranjit