In my case I don't get anything in the logs indicating that the kernel is trying to talk to mmc1.
$ dmesg | grep mmc [ 4.594995] mmc0: sdhost-bcm2835 loaded - DMA enabled (>1) [ 4.603742] mmc-bcm2835 3f300000.mmc: mmc_debug:0 mmc_debug2:0 [ 4.610786] mmc-bcm2835 3f300000.mmc: DMA channel allocated [ 4.706210] mmc0: host does not support reading read-only switch, assuming write-enable [ 4.805580] mmc0: new high speed SDHC card at address aaaa [ 4.806124] mmcblk0: mmc0:aaaa SL32G 29.7 GiB [ 4.817997] mmcblk0: p1 p2 [ 5.574715] EXT4-fs (mmcblk0p2): couldn't mount as ext3 due to feature incompatibilities [ 5.589925] EXT4-fs (mmcblk0p2): couldn't mount as ext2 due to feature incompatibilities [ 5.620475] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: errors=remount-ro [ 5.709751] EXT4-fs (mmcblk0p2): couldn't mount as ext3 due to feature incompatibilities [ 5.725000] EXT4-fs (mmcblk0p2): couldn't mount as ext2 due to feature incompatibilities [ 5.754792] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null) [ 6.399854] FAT-fs (mmcblk0p1): IO charset ascii not found $ snap list Name Version Rev Tracking Publisher Notes cm3 16.04-0.7 7 edge canonical✓ gadget core 16-2.42.2+git1570.35c66d9 8199 edge canonical✓ core nano 3.2+pkg-24de 29 stable snapcrafters - pi2-kernel 4.4.0-1126.135 104 edge canonical✓ kernel $ find /proc/device-tree/ | grep sdio /proc/device-tree/soc/gpio@7e200000/sdio_pins /proc/device-tree/soc/gpio@7e200000/sdio_pins/name /proc/device-tree/soc/gpio@7e200000/sdio_pins/phandle /proc/device-tree/soc/gpio@7e200000/sdio_pins/brcm,function /proc/device-tree/soc/gpio@7e200000/sdio_pins/brcm,pins /proc/device-tree/soc/gpio@7e200000/sdio_pins/brcm,pull /proc/device-tree/soc/gpio@7e200000/sdio_pins/linux,phandle -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux-raspi2 in Ubuntu. https://bugs.launchpad.net/bugs/1823655 Title: Second SD card on RPi3 CM3 on Ubuntu Core 18 does not work Status in linux-raspi2 package in Ubuntu: In Progress Status in linux-raspi2 source package in Bionic: New Bug description: As suggested in following thread; https://forum.snapcraft.io/t/second-sd-card-on-rpi3-cm3-with-ubuntu- core-18/10465 a bug report. The configuration works for a Ubuntu Core 16 device. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-raspi2/+bug/1823655/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
