BeagleBone Black MMC ordering clashes
Ian Lepore
ian at freebsd.org
Mon Jan 9 02:15:29 UTC 2017
On Fri, 2017-01-06 at 16:40 -0200, Dr. Rolf Jansen wrote:
> >
> > Am 06.01.2017 um 15:09 schrieb Ian Lepore <ian at freebsd.org>:
> >
> > On Fri, 2017-01-06 at 14:33 -0200, Dr. Rolf Jansen wrote:
> > >
> > > >
> > > >
> > > > Am 06.01.2017 um 13:54 schrieb Ian Lepore <ian at freebsd.org>:
> > > >
> > > > On Fri, 2017-01-06 at 12:37 -0200, Dr. Rolf Jansen wrote:
> > > > >
> > > > >
> > > > > The BeagleBone Black comes with 2 MMC facilities, one built-
> > > > > in
> > > > > (internal 4 GB) and one provided by a removable SD card. For
> > > > > unknown
> > > > > reasons the BBB defined on the removable SD card to be MMC0
> > > > > and
> > > > > the
> > > > > internal flash memory is MMC0.
> > > > >
> > > > > 1) In the first go, I dd'd the FreeBSD-12 BBB snapshot
> > > > > (20161221)
> > > > > onto a SD card and I was able to start the device from that
> > > > > card.
> > > > > gpart showed me that the device identifier of the SD card is
> > > > > mmcsd0
> > > > > and that of the internal flash memory is mmcsd1. OK, that
> > > > > matches
> > > > > the
> > > > > already mentioned definitions.
> > > > >
> > > > > 2) Now, I destroyed the partition of the internal mmcsd1
> > > > > and
> > > > > created a new one:
> > > > >
> > > > > => 63 7552961 mmcsd1 MBR (3.6G)
> > > > > 63 8129 - free - (4.0M)
> > > > > 8192 8192 1 fat32 [active] (4.0M)
> > > > > 16384 7536640 2 freebsd (3.6G)
> > > > >
> > > > > => 0 7536640 mmcsd1s2 BSD (3.6G)
> > > > > 0 7536640 1 freebsd-ufs (3.6G)
> > > > >
> > > > > 3) I copied over the contents of /boot/msdos from the
> > > > > external
> > > > > SD
> > > > > card to the msdosfs on mmcsd1s1 and I installed the FreeBSD
> > > > > 12
> > > > > snapshot on mmcsd1s1a. Restarting the device from the
> > > > > internal
> > > > > flash
> > > > > and no external SD inserted with FreeBSD 12-CURRENT works
> > > > > well at
> > > > > the
> > > > > first glance.
> > > > >
> > > > > 4) However, the internal flash got now the device
> > > > > identifier
> > > > > mmcsd0:
> > > > >
> > > > > ...
> > > > > mmc0: No compatible cards found on bus
> > > > > ...
> > > > > mmcsd0: 4GB <MMCHC MMC04G 5.8 SN 82390DEC MFG 11/1998 by
> > > > > 112
> > > > > 0x0000> at mmc1 48.0MHz/8bit/65535-block
> > > > > ...
> > > > >
> > > > > I know, this is how FreeBSD deals with the device numbering,
> > > > > i.e.
> > > > > serial numbers starting at zero without particular meaning,
> > > > > and I
> > > > > know that we should not rely on the number ordering.
> > > > >
> > > > > But it seems that the MMC device driver does cont on the
> > > > > external
> > > > > SD
> > > > > card is at MMC0 when I insert it into the BBB once it has
> > > > > been
> > > > > started from the internal flash. It seems to insist to assign
> > > > > the
> > > > > device ID mmcsd0, which results in the device ordering clash
> > > > > because
> > > > > mmcsd0 has been assigned to the internal flash at MMC1 (s.
> > > > > above).
> > > > >
> > > > > In the moment, I can have both flash device active at the
> > > > > same
> > > > > time
> > > > > only when I start the BBB from the external SD.
> > > > >
> > > > > I would be glad to hear suggestions on how to deal with the
> > > > > issue. At
> > > > > the end of the day, I want to start the device from the
> > > > > mostly
> > > > > static
> > > > > OS file system on the internal flash and keep the volatile
> > > > > data
> > > > > on
> > > > > the external SD.
> > > > >
> > > > > Best regards
> > > > >
> > > > > Rolf
> > > > The mmcsd0 identifier will be assigned to the first mmc device
> > > > found
> > > > that has a valid mmc or sd card. If the external slot has a
> > > > card
> > > > in
> > > > it, it will become mmcsd0 because it gets probed first. If it
> > > > has
> > > > no
> > > > card in it, the onboard eMMC becomes mmcsd0 because the sd slot
> > > > didn't
> > > > claim that device id. There is no way to change the order of
> > > > probing;
> > > > probing happens in order of the devices in the chip. The BBB
> > > > makers
> > > > decided to connect the external sd to the first device and the
> > > > onboard
> > > > eMMC to the second one.
> > > Thank you for rephrasing of what I wanted to say in my initial
> > > post:
> > >
> > > >
> > > >
> > > > >
> > > > >
> > > > > I know, this is how FreeBSD deals with the device numbering,
> > > > > i.e.
> > > > > serial numbers starting at zero without particular meaning,
> > > > > and I
> > > > > know that we should not rely on the number ordering.
> > > So, yes, this part is absolutely clear and understood.
> > >
> > > >
> > > >
> > > > If you want the eMMC to be the root filesystem whether there is
> > > > an
> > > > external sd card installed or not, the only solution is to use
> > > > UFS
> > > > or
> > > > GPT labels instead of device names to refer to partitions in
> > > > fstab.
> > > I do not rely on device identifiers in fstab on non of my
> > > numerous
> > > FreeBSD boxes, instead, I use the various sorts of labels ever
> > > since,
> > > and I continue to do it also with the BBB installation(s).
> > >
> > > # df -h
> > > Filesystem Size Used Avail Capacity Mounted on
> > > /dev/ufs/SYSTEM 13G 875M 11G 7% /
> > > devfs 1.0K 1.0K 0B 100% /dev
> > > /dev/label/BOOT 4.0M 924K 3.1M 23% /boot/msdos
> > > tmpfs 50M 4.0K 50M 0% /tmp
> > >
> > > However, this does not help in the given case, because the MMC
> > > device
> > > driver refuses to enumerate the SD card when inserted into a BBB
> > > that
> > > has been already started-up from the internal flash. So the
> > > question
> > > is, how can I get the SD card activated once inserted into a
> > > running
> > > system, and I would happily live with any device identifier for
> > > it,
> > > even let it mmcsd77 if only the device would be accessible by
> > > this.
> > >
> > > Best regards
> > >
> > > Rolf
> > Oh, you mean you boot from eMMC without an sd card, then later when
> > you
> > insert an sd card it's not detected? I've never tried that (I've
> > never
> > used the onboard eMMC at all), but it wouldn't surprise me that
> > it's
> > broken.
> Yes, that is the problem.
>
> >
> > It would imply we're not handling the card-detect properly,
> > probably because it's a gpio pin, and we didn't have good gpio
> > support
> > back when I was working on the TI sdcard driver.
> Well, this might be related to an issues with the U-Boot/MLO
> facility. Remember that I replaced the factory one on the eMMC by the
> one from the FreeBSD 12.0-CURRENT(Beaglebone) image. Actually this
> allows me to boot FreeBSD from the internal eMMC without an SD card,
> however with a remarkable notice at the very beginning of the boot
> sequence:
>
> U-Boot SPL 2016.05 (Dec 21 2016 - 18:05:07)
> Trying to boot from MMC2
> Card did not respond to voltage select!
> *** Warning - MMC init failed, using default environment
>
> The "Card did not respond" notice and the consecutive warning does
> not appear when I boot from the SD card, instead I see another one
> about a not supported property by the SD card:
>
> U-Boot SPL 2016.05 (Dec 21 2016 - 18:05:07)
> Trying to boot from MMC1
> Card doesn't support part_switch
> MMC partition switch failed
> *** Warning - MMC partition switch failed, using default
> environment
>
> Perhaps U-Boot disables/deactivates/turns-off something on the board
> already in the very early stage. Perhaps I need to adapt the U-Boot
> image for internal eMMC booting.
>
> >
> > Yep, I just looked at the source, and there's no handling for gpio-
> > based sd card detect in the TI driver. Maybe I can find some time
> > this
> > weekend to add it, now that we have a better gpio infrastructure
> > for
> > drivers to use.
> Many thanks in advance for spending your time.
>
> Best regards
>
> Rolf
Okay, I got this all done and tested this weekend, and just committed
all the changes for am335x (beaglebone) and imx6 (wandboard, cubox,
etc). It's pretty easy to convert an existing driver, so I expect
other boards with sdhci-compatible hardware to get updated soon too.
If you are set up to build custom kernels, you just need to update your
sources to r311736 or later and rebuild. Otherwise you can wait until
the next 12-current snapshot is available (I think those still come out
weekly).
-- Ian
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