Hi Ulf,

thanks again for the heads up.

> Let's first take a step back, because I don't know how the HW busy
> detection works for your controller.
> 
> I have noticed there is TMIO_STAT_CMD_BUSY bit being set for some
> variants, which seems to cause renesas_sdhi_wait_idle() to loop for a
> pre-defined number of loops/timeout. This looks scary, but I can't
> tell if it's really a problem.

That should be okay. The datasheet mentions that some registers can only
be accessed when either CBSY or SCLKDIVEN bits signal non-busyness.
renesas_sdhi_wait_idle() is for that.

> BTW, do you know what TMIO_STAT_CMD_BUSY actually is monitoring?

0: A command sequence has been completed.
1: A command sequence is being executed.

> I have also noticed that MMC_CAP_WAIT_WHILE_BUSY isn't set for any of
> the renesas/tmio variant hosts. Is that simply because the HW doesn't
> support this? Or because implementation is missing?

Good thing we use public development. I recalled we discussed this
before but I needed a search engine to find it again:

https://patchwork.kernel.org/patch/8114821/

Summary: The HW (at least since Gen2) has HW support for busy timeout
detection but I never came around to implement it (and even forgot about
it :( ). So, we still use a workqueue for it.

Kind regards,

   Wolfram