Re: [RFC 0/2] Set mmc(blk)X with DT alias

[Steffen Trumtrar <s.trumtrar@pengutronix.de>]

On Thu, Jul 25, 2013 at 10:28:38AM -0700, Stephen Warren wrote:
> On 07/24/2013 02:09 AM, Steffen Trumtrar wrote:
> > Hi!
> > 
> > Embedded devices often use multiple SD/MMC devices as boot/rootfs disks.
> > Some of them are removable, some not. If the removable cards are not
> > present, but are probed before the non-removable ones, the indexing
> > scheme changes. This makes it harder to hard-code the rootfs in the
> > cmdline.
> >
> > First solution I came up with was the alias-node in DT.
> > I guess my implementation is pretty hacky and ugly, but you can get lost
> > pretty fast in the whole mmc stack.
> > For example, the second patch should use "card->host->index" instead of parsing
> > the alias again, I guess. I'm not sure why it currently doesn't though.
> 
> This has been discussed a few times before and rejected IIRC. One issue
> is that block device ID is actually decoupled from host controller ID
> anyway, e.g. if a removable device is mounted, removed, and then
> re-plugged the new device can get a different ID, so this approach
> doesn't really work in all cases anyway.
> 

Hm, okay. I actually wasn't aware of the older discussions.

> > So, if there is a better place or solution to specify a reliable ordering
> > of mmc devices, please let me hear it.
> 
> root=UUID=xxx or root=PARTUUID=xxx are the best solution. With recent
> U-Boot, you can enable and use the "part" command to find the partition
> UUID automatically, and hence not need to hard-code anything. Something
> similar could presumably be implemented for other bootloaders.

I am actually okay with that. I know barebox can do that, but didn't knew that
U-Boot is also capabable of that.
So, I'm okay with dropping the patch.

Thanks,
Steffen

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