On Thu, Jun 15, 2017 at 02:12:58PM +0200, Linus Walleij wrote:

Currently the RPMB partition spawns a separate block device
named /dev/mmcblkNrpmb for each device with an RPMB partition,
including the creation of a block queue with its own kernel
thread and all overhead associated with this. On the Ux500
HREFv60 platform, for example, the two eMMCs means that two
block queues with separate threads are created for no use
whatsoever.

Yikes!  What an amazingly stupid design decision.

This patch tries to amend the situation using the following
strategy:

- Stop creating a block device for the RPMB partition/area

- Instead create a custom, dynamic character device with
  the same name.

- Make this new character device support exactly the same
  set of ioctl()s as the old block device.

- Wrap the requests back to the same ioctl() handlers, but
  issue them on the block queue of the main partition/area,
  i.e. /dev/mmcblkN

Is it really worth to add all this code to work around the issue?
We could still keep the block device around and stub out anything
not needed.

Tomas Winkler [off-list ref]
Signed-off-by: Linus Walleij <redacted>

I think some tag is missing before Tomas' name.