Re: [PATCH 4/5] spi: spi-nxp-fspi: add function to select sample clock source for flash reading

[Michael Walle <mwalle@xxxxxxxxxx>]

> From: Haibo Chen <haibo.chen@xxxxxxx>
> 
> fspi define four mode for sample clock source selection.
> 
> Here is the list of modes:
> mode 0: Dummy Read strobe generated by FlexSPI Controller and loopback internally
> mode 1: Dummy Read strobe generated by FlexSPI Controller and loopback from DQS pad
> mode 2: Reserved
> mode 3: Flash provided Read strobe and input from DQS pad
> 
> In default, fspi use mode 0 after reset.
> For 8-8-8-DTR mode, need to use mode 3, otherwise 8-8-8-DTR read always
> get incorrect data.

I'd say this is board dependant, right? If you now hardcode 8d8d8d
to always use mode 3. I'm not sure how a board which doesn't have
the DQS connected to the flash can change this to another mode
again. Looks like we'd need a (DT) property which tells you if
there is actually a DQS line connected to the flash.

Btw you don't check buswidth, so you'll enable that mode for any
DTR mode.

-michael