[FS#646] MMC/SD - mount/read/write not possible -> kernel errors

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - camel (camel) 

Attached to Project - LEDE Project
Summary - MMC/SD - mount/read/write not possible -> kernel errors
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Supply the following if possible:
- Device problem occurs on
- Software versions of LEDE release: Powered by LuCI Master (git-17.078.53745-180f2d6) / LEDE Reboot SNAPSHOT r3792-0685f2a

reproduce:

MMC card found on boot:
root at router:~# logread|grep -i mmc
Mon Mar 20 12:54:57 2017 kern.info kernel: [    6.680000] mmc0: new high speed SDHC card at address 0001
Mon Mar 20 12:54:57 2017 kern.info kernel: [    6.690000] mmcblk0: mmc0:0001 00000 29.8 GiB


but if i try to mount/read/write to it ... still not possible and kernel errors ....
root at router:~# fdisk -l

Disk /dev/mmcblk0: 29.8 GiB, 32010928128 bytes, 62521344 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

root at router:~# fdisk /dev/mmcblk0

Welcome to fdisk (util-linux 2.28).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0xf924301d.

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-62521343, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-62521343, default 62521343):

Created a new partition 1 of type 'Linux' and of size 29.8 GiB.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

##################
logcat ....
Mon Mar 20 15:58:53 2017 kern.err kernel: [  393.680000] msdc-1 -> cmd resp  cmd resp  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BWRITE DSPL DATWRDL                                                                                                       Y MSDC_DAT_RDDLY0  TUNE_BREAD dcrc DATRDD                                                                                                       LY0/1 dsmpl