[Ksummit-discuss] [TECH TOPIC] (PCI) driver rebinding

[Leon Romanovsky]

On Sun, Jun 25, 2017 at 05:39:34PM +0200, Hannes Reinecke wrote:
> Hi all,
>
> here's a thing which came up recently on the SCSI ml:
>
> How should we handle devices with _several_ possible drivers?
>
> Case in point are some HBAs, for which the plan is to have distinct
> drivers for either target or initiator mode.
>
> There are several options how this could be handled:
> - Have a default driver, and manually rebind the 'real' driver once the
> configuration could be read and acted upon.
> That would have the drawback that we do an initialisation in the 'wrong'
> mode, and later have to switch configuration. Which at best will 'just'
> induce some pointless initialisation, at worst confuse attached devices
> to no end. Not to mention introducing lots of interesting races with
> udev and systemd
> - Inhibit default binding, and load the correct drivers after the
> configuration has been read.
> Would be a deviation from the original scenario (where the driver are
> bound/loaded as soon as the device becomes available). Has the drawback
> that one would need to inhibit automatic bindings on the _bus_ level (ie
> PCI), which will be even more interesting.
> - Add some bus-specific (or even general?) device configuration syntax,
> which would allow to pass in the required configuration from the
> command-line (or reasonably early, anyway). For which we need a syntax
> first, anyway. And need to figure out if we can have an abstract syntax
> or would need to have a bus- (or even driver-) specific configuration.

It sounds very similar to devlink, despite that tool was originally introduced
to net and intended for switches, it works on PCI level with BUS_NAME/BUS_ADDRESS
as an handle.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bfcd3a46617209454cfc0947ab093e37fd1e84ef

>
> So no easy way out here, and it might be worth having input from other
> parties. And some might have similar problems (just thinking of
> usb-modeswitch ...), so there might be some synergies to be had.
>
> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke		   Teamlead Storage & Networking
> hare at suse.com			               +49 911 74053 688
> SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
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