[Bug 204521] [new driver] [request] Port rtsx from OpenBSD to FreeBSD

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204521

--- Comment #33 from Gary Jennejohn <gljennjohn at gmail.com> ---
I tried implementing rtsx_xfer_bounce() from the OpenBSD code.

OpenBSD uses this function when the upstream code does not pass in a list of
DMA scatter-gather addresses.  Normally, the SD code in OpenBSD allocates its
own DMA buffers and passes them to the driver.

Since FreeBSD does not do that - it either uses buffers on the kernel stack or
buffers from a struct bio - it seemed logical to me to try rtsx_xfer_bouce().

The DMA transfer raises an interrupt, but the target buffer is always filled
with 0s.

I'm running out of ideas on how to get DMA to work.

If I had a laptop I could tear apart I'd put a logic analyzer on the controller
pins and compare the behavior between OpenBSD and FreeBSD.  Unfortunately, the
laptop I have is a loaner and I can't do that.

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