Mount root from SD card?
Alexander Motin
mav at FreeBSD.org
Tue Jan 20 11:29:35 PST 2009
M. Warner Losh wrote:
> In message: <4976215B.40302 at FreeBSD.org>
> Alexander Motin <mav at FreeBSD.org> writes:
> : M. Warner Losh wrote:
> : > In message: <49760E8E.1000609 at FreeBSD.org>
> : > Alexander Motin <mav at FreeBSD.org> writes:
> : > : Krassimir Slavchev wrote:
> : > : > -----BEGIN PGP SIGNED MESSAGE-----
> : > : > Hash: SHA1
> : > : >
> : > : > 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.
> : >
> : > This controller's driver should do the right thing when given a too
> : > high bus speed: clamp it to the maximum...
> : >
> : > However, maybe the clamps are right. The above symptom was what I'd
> : > see when the data read in was corrupted. It is the whole reason I
> : > never enabled the multi-block read for this controller. I could never
> : > make it work well enough to even make mountroot happy.
> :
> : High-speed timings does not mean just a high frequency. It is some
> : different signaling scheme required for higher frequencies, which should
> : be explicitly enabled on both card and controller. If one of them is not
> : enabled - there will be problems.
>
> Ah, true. That does need to be a capability then.
>
> : > : 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.
> : >
> : > It is initialized to zero. It is expected that there will be a
> : > different mechanism in the future to set it generically on a per-board
> : > basis.
> :
> : 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.
Bug of not working 4-bit mode? I have told why it is not working:
because zeroed wire4 variable permanently disables it by clearing
respective bit in controller SDCR register. I can't imagine any possible
usage for this variable in present state. Can you?
--
Alexander Motin
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