Devicetree: Initialization order of mmc block devices?

[Jassi Brar]

On 18 July 2012 19:41, Knut Wohlrab <knut.wohlrab at de.bosch.com> wrote:
> On 07/18/2012 03:47 PM, Jassi Brar wrote:
>>
>> On 18 July 2012 15:19, Knut Wohlrab <knut.wohlrab at de.bosch.com> wrote:
>>
>>> If a SD card is inserted at boot time, its "mmcblk0", the embedded
>>> MMC (eMMC) device "mmcblk1".  This makes it difficult to give the kernel
>>> the
>>> correct device for the eMMC root file system ("root=/dev/mmcblk?p1 ...").
>>>
>> How about  root=UUID=<eMMC-partition>  ?
>
> Because we are talking about an embedded device, it is very difficult to get
> a UUID of a eMMC partition into kernel command line with U-Boot. Handling of
> UUID is also a big effort at board manufacturing.
>
I don't realize how bad is it if a common UUID is used on each cloned
eMMC(non-removable) of every instance of a device. But of course only
you know what's best for your product.

>
> This problem can occur on many devices with embedded MMC and removable SD,
> e.g. smart phones. So I think we should find an solution to define MMC scan
> order or device number/name in a device tree.
>
I assume your issue is that due to async nature of mmc scanning, the
eMMC is detected later than external card, despite being the probe for
eMMC's slot initiated first ?
If so, we can do by simply associating 'N' of 'mmcblkN' with the slot
index i.e, mmc_host.index (instead of mmc_blk_data.name_idx). Which is
always in the order of probe calling. And we don't need to modify, or
expect more of, DT for that. Though I suspect there must be some
serious reason why it's not already done that way.