Mount root from SD card?

[Alexander Motin]

Alexander Motin wrote:
> M. Warner Losh wrote:
>> In message: <20090120.122312.1543793985.imp at bsdimp.com>
>>             "M. Warner Losh" <imp at bsdimp.com> writes:
>> : : IMHO it is incorrect to disable 4bit mode on that stage, it is too 
>> late : : there. It should be done at controller capabilities 
>> announcement stage. : : If you are not objecting, I would remove that 
>> wire4 variable.
>> : : I am objecting.  The code is there so that the rest of the driver 
>> does
>> : the right thing when doing 4-bit.  It needs to be a capability too.
>> : : However, before we go monkeying with this, we need to find the
>> : underlying bug.
>>
>> I've got the following patch, untested, that I think does what I think
>> needs to be done.  Not sure about the return value from update_ios...
>>
>> Index: at91_mci.c
>> ===================================================================
>> --- at91_mci.c    (revision 187479)
>> +++ at91_mci.c    (working copy)
>> @@ -201,7 +201,10 @@
>>      sc->host.f_min = 375000;
>>      sc->host.f_max = 30000000;
>>      sc->host.host_ocr = MMC_OCR_320_330 | MMC_OCR_330_340;
>> -    sc->host.caps = MMC_CAP_4_BIT_DATA;
>> +    if (sc->wire4)
>> +        sc->host.caps = MMC_CAP_4_BIT_DATA;
>> +    else
>> +        sc->host.caps = 0;
>>      child = device_add_child(dev, "mmc", 0);
>>      device_set_ivars(dev, &sc->host);
>>      err = bus_generic_attach(dev);
> 
> Ok. I agree with this part. If for some reason you really need this 
> wire4 variable, this is the right way to use it.
> 
>> @@ -295,6 +298,8 @@
>>              clkdiv = (at91_master_clock / ios->clock) / 2;
>>      }
>>      if (ios->bus_width == bus_width_4 && sc->wire4)
>> +        return EINVAL;
>> +    if (ios->bus_width == bus_width_4)
>>          WR4(sc, MCI_SDCR, RD4(sc, MCI_SDCR) | MCI_SDCR_SDCBUS);
>>      else
>>          WR4(sc, MCI_SDCR, RD4(sc, MCI_SDCR) & ~MCI_SDCR_SDCBUS);
>>
> 
> This part is correct, but useless. If the first part have not set 
> MMC_CAP_4_BIT_DATA, then mmc layer will never request bus_width_4. 
> That's why I have proposed to remove " && sc->wire4" check from here.

No, stop, this part is incorrect. Correct but useless would be:

     if (ios->bus_width == bus_width_4 && !sc->wire4)
         return EINVAL;

-- 
Alexander Motin