[Bug 29633] Ubuntu kernel handles mmc devices incorrectly

[Johan Brannlund]

Public bug reported:
https://launchpad.net/malone/bugs/29633

Affects: linux-source-2.6.15 (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

Description:
The Ubuntu kernel 2.6.15-13-amd64-k8 does not handle mmc devices
correctly, even though it includes the sdhci patch by Pierre Ossman. A
vanilla 2.6.15 kernel + sdhci patches handles the devices correctly and
I am able to use the SD card reader on my system.

In slightly more detail, the problem is this:

In both kernels (ubuntu and standard), the end of /proc/devices looks
like

252 mmc
253 device-mapper
254 mdp

Both kernels also produce a device node that looks like

brw-rw---- 1 root disk 253, 0 2006-01-25 01:03 /dev/mmcblk0

However, the stock 2.6.15 also shows me a mountable partition device:

brw-rw---- 1 root disk 253, 1 2006-01-25 01:03 /dev/mmcblk0p1

mmcblk0p1 does NOT appear with the Ubuntu kernel.

Also, with the stock kernel I can read directly off the device with
dd if=/dev/mmcblk0 of=/tmp/blah bs=512 count=1000 and this correctly gives me the beginning of the files on the memory card.

With the Ubuntu kernel, the dd command produces  a file that seems to be
the beginning of my swap space:

# strings /tmp/blah |more
SWAPSPACE2SWAPSPACE2
[]A\A]
ATUSH
[]A\
upIc
AWAVAUATUSH
DUff
[...]

Note that in both kernels, the mmcblk0 device node has a major number of
253 while /proc/devices shows that mmc should be 252. However, this does
not prevent the stock kernel from correctly reading the card.

Attempting to recreate the device node with major number 252 under the
Ubuntu kernel and then reading from it with dd gives me an error
message:

dd: opening `/dev/mmcblk0': No such device or address