Re: PCI Rescan Question

[Lukas Wunner <lukas@wunner.de>]

On Wed, Apr 26, 2017 at 03:56:09PM -0700, Kyle Gale wrote:
> Can someone help me understand why I need to remove my stale PCI
> device files from the tree if I want to properly get my device
> re-initialized after unplugging and reinserting?
> 
> For example, I turn on my system with my PCI device plugged in. All is
> fine. I unplug it, plug it back in, and rescan (echo 1 >
> /sys/bus/pci/devices/rescan) and end up in this state where my BAR0 is
> not set, and other things are not entirely correct.
> 
> But if I do a remove (echo 1 > /sys/bus/pci/devices/xxxx/xx.x/remove)
> of the port, it then properly re-initializes my device when I do a
> rescan.
> 
> Why does it not suffice to simply do a rescan? Does the rescan skip
> some step if it finds that the device is already in the PCI tree? It's
> not as if the rescan completely skips the device if I don't do a
> remove, it just doesn't do all of the initialization.

Initiating a rescan via sysfs results in a call to pci_rescan_bus(),
which only adds devices but doesn't remove any.  I guess it can be
argued that this behavior is counter-intuitive and should be changed.

Thanks,

Lukas