Mount root from SD card?

[Alexander Motin]

Alexander Motin wrote:
> 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.

As I can see from specification, if sc->wire4 is set to 0 by default, 
bus will not ever switched into 4bit mode. Try to just comment out " && 
sc->wire4" part of at91_mci.c. If this variable expected to report real 
bus width, then it probably should be done in different way, by 
reporting correct host capabilities.

> 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