Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree

Stefan Agner
2019-03-17T15:05:14Z

On 16.03.2019 16:39, Russell King - ARM Linux admin wrote:
> On Sat, Mar 16, 2019 at 01:33:58PM +0100, Marek Vasut wrote:
>> If you have a FS or partition table there, it does.
>> If you don't, I agree ... that's a problem.
>
> eMMC boot partitions are called mmcblkXbootY, and unless you have more
> than one eMMC device on the system, they can be found either by looking
> for /dev/mmcblk*boot* or by querying udev. The advantage of using udev
> is you can discover the physical device behind it by looking at DEVPATH,
> ID_PATH, etc, but you may not have that installed on an embedded device.
>
> However, as I say, just looking for /dev/mmcblk*boot* is sufficient to
> find the eMMC boot partitions where there is just one eMMC device
> present (which seems to be the standard setup.)
>
>> > I don't care the slightest what the numbering is, as long as it is
>> > stable. On some hardware, with an unpatched kernel, the mmc device
>> > numbering changes depending on whether or not an SD card is inserted on
>> > boot. Getting rid of that behaviour is really all I want.
>>
>> Agreed, that would be an improvement.
>
> The mmc device numbering was tied to the mmc host numbering a while back
> and the order that the hosts are probed should be completely independent
> of whether a card is inserted or not:
>
> snprintf(md->disk->disk_name, sizeof(md->disk->disk_name),
> "mmcblk%u%s", card->host->index, subname ? subname : "");
>
> snprintf(rpmb_name, sizeof(rpmb_name),
> "mmcblk%u%s", card->host->index, subname ? subname : "");
>
> I suspect that Mans is quoting something from the dim and distant past
> to confuse the issue - as shown above, it is now dependent on the host
> numbering order not the order in which cards are inserted.

Commit 9aaf3437aa72 ("mmc: block: Use the mmc host device index as the
mmcblk device index") which came in with v4.6 enables constant mmc block
device numbering. I can confirm that it works nicely, and it improved
the situation a lot.

That being said, we still use a patch downstream which allows
renumbering using an alias. We deal with a bunch of different boards
with different SoC's. I have a couple of SD cards with various rootfs
and use internal eMMC boot quite often as well. Remembering which board
uses which numbering is a pain. Maintaining a patch is just easier...
Furthermore, U-Boot allows reordering and all boards I deal with use mmc
0 for the internal eMMC. The aliases allow consistency.

--
Stefan