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

[Greg KH <gregkh@linuxfoundation.org>]

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?

Go kick the hardware developers for trying to come up with such complex
beasts :)

> 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.

Yes, do this.

> 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

How will udev and systemd have "races"?  We do this today all the time
in USB with the usb-modeswitch userspace code, as you point out.

> - Inhibit default binding, and load the correct drivers after the
> configuration has been read.

You can do that too vfio does it from what I recall.  It's easy in that
you can just not do a MODULE_DEVICE_TABLE() export and no driver will
automatically be loaded and userspace is required to load what it wants.

> 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.

Hah, good luck with that :)

greg k-h