USB controller enumeration on APU3 is random since the update to kernel 6.6

[Henrique de Moraes Holschuh]

On 18/07/2024 11:47, Sam Kuper wrote:
> After all, the commit message suggests the developer didn't anticipate this commit causing breakage.

More like they don't expect it to cause breakage when a suitable 
userspace solution to the issue of non-deterministic probing order is 
deployed for hotplug handling (and that includes coldplug on hotplug 
buses).  Almost everything else that is a hotplug bus already does this 
(PCIe, SATA, SAS...).

I suppose it would be a regression if it happened to land through a 
stable update, especially if it landed in a LTS kernel.  But if it 
landed on 6.6, I very much doubt it will be reverted.

On typical desktops, you'd use udev to rename the node to something 
static, or add a symlink, etc.

OpenWRT has its hotplug via procd, which is different, but it should 
still be usable for that kind of *required* functionality.  What the 
wiki describes for "usbmisc" hotplug does *not* look good, hopefully the 
wiki is incomplete.  Otherwise, procd should be improved and meanwhile, 
you need to deploy a script to handle that event that does the 
follow-the-symlinks game in sysfs to go from usblp to usb endpoint, and 
get the necessary device data from there.

-- 
Henrique de Moraes Holschuh
Analista de Projetos
Centro de Estudos e Pesquisas em Tecnologias de Redes e Operações 
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