Date: Tue, 20 Jan 2009 12:23:12 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: mav@freebsd.org Cc: freebsd-arm@freebsd.org Subject: Re: Mount root from SD card? Message-ID: <20090120.122312.1543793985.imp@bsdimp.com> In-Reply-To: <4976215B.40302@FreeBSD.org> References: <49760E8E.1000609@FreeBSD.org> <20090120.114051.-854291995.imp@bsdimp.com> <4976215B.40302@FreeBSD.org>
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In message: <4976215B.40302@FreeBSD.org>
Alexander Motin <mav@FreeBSD.org> writes:
: M. Warner Losh wrote:
: > In message: <49760E8E.1000609@FreeBSD.org>
: > Alexander Motin <mav@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.
Warner
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