Hi Adam,

I am very sorry that it took so long until I am now able to respond.
First, too many other duties with higher priority came in. Second, the
card didn't fail 100% for me after all which made debugging still
challenging. But it failed often enough, so I at least have a pointer
now.

> From what I have been able to determine, the U-Boot code explicitly
> disables DMA during the tuning phase:

...

> However, Linux does not disable the DMA, and the value of taps is zero
> and the tuning ultimately fails.

I disabled DMA while tuning but it did not help. It finally turns out
that adding a delay after each tuning command seems to help. U-Boot does
this but Marek (the driver author for U-Boot) cannot recall why he added
the delay. I'll send a patch in some minutes.

All the best,

   Wolfram