quoted

The timing phase is no more needed since the auto tuning is applied.

I feel this is unwise: we're now ignoring constraints set in the devicetree.
Auto-tuning is fine, but I think that should be a feature that new platforms can
exploit by default. Older platforms that do specify the phase values via the
devicetree can be converted at the leisure of their maintainers (by removing
the phase properties).

Support needs to remain in the driver until there are no (aspeed-based)
devicetrees specifying the phases.

The timing phase only works on AST2600 or newer platform which has added a delay cell in the RTL.
The older platform AST2500, AST2400 doesn't support the timing phase.
It supposed no effect on older platform. 
The old manner that a static timing value customized from devicetree is inconvenient because customer needs to check waveform associated with each delay taps. Once the emmc parts changed, a fixed timing value may not work. That's why auto tune here instead of a static value.

Andrew