Date: Fri, 6 Jan 2017 14:33:36 -0200 From: "Dr. Rolf Jansen" <rj@obsigna.com> To: freebsd-arm@freebsd.org Subject: Re: BeagleBone Black MMC ordering clashes Message-ID: <0D800E14-799A-4926-AEF8-CD698D647E40@obsigna.com> In-Reply-To: <1483718084.96230.5.camel@freebsd.org> References: <7D750433-59FC-4999-AC24-041683E17310@obsigna.com> <1483718084.96230.5.camel@freebsd.org>
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> Am 06.01.2017 um 13:54 schrieb Ian Lepore <ian@freebsd.org>: >=20 > 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. >>=20 >> 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. >>=20 >> 2) Now, I destroyed the partition of the internal mmcsd1 and >> created a new one: >>=20 >> =3D> 63 7552961 mmcsd1 MBR (3.6G) >> 63 8129 - free - (4.0M) >> 8192 8192 1 fat32 [active] (4.0M) >> 16384 7536640 2 freebsd (3.6G) >>=20 >> =3D> 0 7536640 mmcsd1s2 BSD (3.6G) >> 0 7536640 1 freebsd-ufs (3.6G) >>=20 >> 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. >>=20 >> 4) However, the internal flash got now the device identifier >> mmcsd0: >>=20 >> ... >> 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 >> ... >>=20 >> 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. >>=20 >> 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). >>=20 >> In the moment, I can have both flash device active at the same time >> only when I start the BBB from the external SD. >>=20 >> 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. >>=20 >> Best regards >>=20 >> Rolf >=20 > 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
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