LS1027A (LS1028) FSPI not working at 100+ MHz speeds

[mikelooijmans]

We've a cusom LS1027 board, with a fast QSPI NOR chip connected to the FSPI interface. The chip can transfer 4-wire data at 166MHz.

When I set this in the devicetree as max-frequency, it doesn't work properly and the driver outputs this message:
DLL lock failed, please fix it!

If I change the max-frequency to 50MHz, everything works, but the speed is way lower than it ought to be (obviously). I'd be happy to "fix it" but there's no clue whatsoever as to what the problem is.

I noticed that on our LS1028ARDB board, the frequency has also been limited to only 50 MHz, and the behavior is the same, it also outputs this error if I up the frequency.

What's up with the FSPI? It's supposed to go much higher than 50MHz, but apparently not in the real world?

[SebastianG]

Hi @mikelooijmans,

Apologies for the delayed response,

Could you please share with me a image from the signals of FSPI when the frequency goes down?

Regards

[mikelooijmans]

I would if I had any idea what you mean by that.

The issue here is documentation.

Looks like the driver needs to support RX mode "1" for some configurations (like ours), but the documentation is unclear on what mode to use when.

Also, what is the max speed the controller supports? Our NOR flash chip supports 166 MHz (SDR) so it should be possible to go higher.

[SebastianG]

Hi @mikelooijmans,

According to the datasheet the maximum speed of the controller FlexSPI is 100 MHz 

Regards

[SebastianG]

Hi @mikelooijmans,

I am already working on your question, when I have any update I will let you know

Regards

[mikelooijmans]

If I patch the driver to use RX mode "1" instead of "0", it works at 100 MHz. It's unclear from the datasheet what speeds are supposed to work in what mode, and how the RDS pin is to be used.