specifying order of /dev/mmcblk devices via device-tree?

On 2016-11-16 06:45, Ulf Hansson wrote:

On 28 October 2016 at 17:37, Mark Rutland [off-list ref] wrote:

quoted

On Fri, Oct 28, 2016 at 08:23:04AM -0700, Tim Harvey wrote:

quoted

Greetings,

I have an IMX6 board that has the following:
sdhc1: mmc0: sdio radio
sdhc2: mmc1: /dev/mmcblk1: microSD connector
sdhc3: mmc2: /dev/mmcblk2: on-board eMMC

I would like to have sdhc3 registered as /dev/mmcblk0 and sdhc2
registered as /dev/mmcblk1 so that permanent storage is the first
mmcblk device as I think this is more intuitive however currently
these get instanced in the order they appear in the imx6qdl.dtsi
device-tree configuration and are not able to be mapped the way I want
them in my dts file.

Is there a way, or if not is there a desire for a way, to specify the
order of /dev/mmcblk devices via device-tree?

As with many other devices, there is no standard way of controlling the
Linux enumeration (and given the ID space is shared with other dynamic
devices it's not something that could generally work).

These should be refererd to by UUID if possible.

If not, we could cosider adding a by-dt-path or something like that.

So does that mean you think using "DT aliases" would be okay? As
Javier pointed out, there have been some attempts [1] for that, but
they didn't make it.
Perhaps we need to re-consider, and if so please re-review the DT
bindings patch from that series.

I really would like to see some sort of stable MMC block device
ordering.

by-dt-path solutions requires initramfs, which adds complexity and boot
time. Both not very welcome in simple embedded devices.

PARTUUID is relying on a particular instance of a partition, which is
not the same as to say boot from the second partition of device X.

The main problem I see in my patchset is that it works around the fact
MMC is a bus. Adding the mmc controller number to the block device name
would avoid that issue (mmc0blk0...), not sure if a such a drastic
change would be acceptable.

--
Stefan