Mount root from SD card?

[Alexander Motin]

Krassimir Slavchev wrote:
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> M. Warner Losh wrote:
> ...
>> mmcsd0: 1983MB <SD Memory Card> at mmc0 30MHz/1bit
>> Trying to mount root from ufs:/dev/mmcsd0s1
>>
>> Manual root filesystem specification:
>>   <fstype>:<device>  Mount <device> using filesystem <fstype>
>>                        eg. ufs:/dev/da0a
>>   ?                  List valid disk boot devices
>>   <empty line>       Abort manual input
>>
>> mountroot> ?
>>
>> List of GEOM managed disk devices:
>>   mmcsd0
>>
>>> Looks like that should be working.
>>> mav@ has done a lot of hacking on the mmc code...
>>> Do you have 1 wire or 4 wires for your mmc bus on your board?
> 
> On the board all 4 bus wires are connected (MCD A0-A3) but I've never
> seen working 4-bit mode on AT91RM9200 (See PR128987 too).

I have just committed MMCBR_IVAR_CAPS implementation into CURRENT. 
Without having it implemented, results can be unpredictable. For 
example, mmc layer could enable high-speed timings to reach 30MHz, but 
this mode is not implemented for this controller. Booting with verbose 
messages enabled could give a bit more information.

What's about 4-bit mode, I see some sc->wire4 variable checked by the 
driver, which is never initialized. I don't very understand how this 
thing expected to work.

PS: For MMC cards bus width testing routine implemented. May be we could 
do something alike for SD cards. It is not part of SD specification, but 
may be we could just issue some other command, transferring data, to 
check effective bus width.

-- 
Alexander Motin