port-arm/50388: Recent sdhc(4) changes break BeagleBone / BeagleBone Black SD cards and eMMC

[jmcneill%invisible.ca@localhost]

>Number:         50388
>Category:       port-arm
>Synopsis:       Recent sdhc(4) changes break BeagleBone / BeagleBone Black SD cards and eMMC
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-arm-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Nov 01 21:15:00 +0000 2015
>Originator:     Jared McNeill
>Release:        7.99.21
>Organization:
NetBSD
>Environment:
NetBSD 7.99.21 (BEAGLEBONE)
>Description:
A -current kernel fails to detect SD card and the eMMC on BeagleBone and BeagleBone Black boards.

> sdhc0 at obio0 addr 0x48060100-0x48060fff intr 64sdhc0: EDMA tx channel 24, rx channel 25: SDHC controller (EDMA)
> sdhc0: SDHC 2.0, rev 49, platform DMA, 96000 kHz, HS 1.8V 3.0V, 1024 byte blocks
> sdmmc0 at sdhc0 slot 0
> ...
> sdmmc_io_send_op_cond: ocr = 0
> sdmmc_io_send_op_cond: error = 60
> sdmmc0: sdmmc_mem_send_op_cond: ocr=0
> sdmmc0: sdmmc_mem_send_op_cond: error=0, ocr=0x40ff8000
> sdmmc0: host_ocr 0x40060060
> sdmmc0: card_ocr 0x40ff8000
> sdmmc0: sdmmc_mem_send_if_cond: error=0, ocr=0x1aa
> sdmmc0: sdmmc_mem_send_op_cond: ocr=0x40060000
> sdmmc0: sdmmc_mem_send_op_cond: error=0, ocr=0xc0ff8000
> sdmmc_dump_data: CID
> --------+--------------------------------------------------+------------------+
> offset  | +0 +1 +2 +3 +4 +5 +6 +7  +8 +9 +a +b +c +d +e +f | data             |
> --------+--------------------------------------------------+------------------+
> 00000000| 93 00 73 b1 f0 76 10 30  30 30 30 30 4d 53 1b 00 | ..s..v.00000MS.. |
> --------+--------------------------------------------------+------------------+
> sdmmc0: mem init failed
> sdmmc0: init failed

I've narrowed this down to revision 1.84 of dev/sdmmc/sdhc.c; a kernel with r1.83 works properly.
>How-To-Repeat:
Boot a -current kernel on BeagleBone or BeagleBone black.
>Fix: