mmci: U300 "sync with blockend" broken for multi-block?

[Linus Walleij]

...and to round off a theory of why the U300 and Ux500 is
missing interrupts:

Maybe the IP-block does not really handle the case of a block
interrupt not being ACK:ed before the next block is ready. So
it will just fire another "1" flag, which gets ACK:ed at the end
of the interrupt handler with the IRQ currently being processed.

So the interrupt handler will unknowingly consume interrupts
for other blocks.

The right way would be to either:

- Queue block ACKs so that they are ACK:ed one at the time
  if the hardware reads ahead. (Which requires a quite deep
  queue on large writes.)

- Hold back further block reading from the card until the IRQ
  has been ACK:ed. (Which is not good for speed.)

So to avoid both it is indeed a logical thing to remove the
block interrupt altogether and just wait for the last one to
avoid trouble, it's just not documented and
HW-implemented as such.

Now I'll send that patch.

Yours,
Linus Walleij