4-bit SD Card mode

[Björn König]

M. Warner Losh wrote:
>> I'm not sure I like this at all.  The devices shouldn't be setting up
>> the pins for that device.  In some cases, they can't know how to do
>> that, and this is one of them.  The device has no way of knowing if
>> all 4 wires are connected, or just 1 and the 'spare' lines are used
>> for GPIO.

and Neil Bradley replied:
> Not doing it will irritate more people (i.e. "I'm not getting full speed
> out of the SD card). While it's a valid concern, I don't think it's
> unrealistic to assume that all 4 DAT lines are hooked up. I've not yet
> encountered a design that A) had SD capabilities, B) was only running
> single bit because of a lack of GPIOs.

Initially I didn't have the problem that "I'm not getting full speed out
of the SD card", but rather that SD Cards doesn't work at all with a
vanilla FreeBSD kernel because nobody configured the PIO for the MCI
controller.

Björn