Mount root from SD card?

[Alexander Motin]

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.

-- 
Alexander Motin