Re: [RFC 1/1] s390/cio: Remove uevent-suppress from css driver

[Halil Pasic <pasic@linux.ibm.com>]

On Mon, 21 Dec 2020 16:46:34 +0100
Cornelia Huck <cohuck@redhat.com> wrote:

> On Sat, 19 Dec 2020 07:33:16 +0100
> Halil Pasic <pasic@linux.ibm.com> wrote:
> 
> > I finally came around to test this. In my experience driverctl works for
> > subchannels and vfio_ccw without this patch, and continues to work with
> > it. I found the code in driverctl that does the unbind and the implicit
> > bind (via drivers_probe after after driver_override was set).
> > 
> > So now I have to ask, how exactly was the original problem diagnosed?
> > 
> > In https://marc.info/?l=linux-s390&m=158591045732735&w=2 there is a
> > paragraph like:
> > 
> > """
> > So while there's definitely a good reason for wanting to delay uevents,
> > it is also introducing problems. One is udev rules for subchannels that
> > are supposed to do something before a driver binds (e.g. setting
> > driver_override to bind an I/O subchannel to vfio_ccw instead of
> > io_subchannel) are not effective, as the ADD uevent will only be
> > generated when the io_subchannel driver is already done with doing all
> > setup. Another one is that only the ADD uevent is generated after
> > uevent suppression is lifted; any other uevents that might have been
> > generated are lost.
> > """
> > 
> > This is not how driverclt works! I.e. it deals with the situation that
> > the I/O subchannel was already bound to the io_subchannel driver at
> > the time the udev rule installed by driverctl activates (via the
> > mechanism I described above).
> 
> That's... weird. It definitely did not work on the LPAR I initially
> tried it out on!
> 

I think Boris told me some weeks ago that it didn't work for him either.
I will check with him after the winter sleep.

> However, I think removing the suppression still looks like a good idea:
> we still have the "any uevent other than ADD will have been lost"
> problem.
> 

I agree. I didn't look into the details, in general I think removing
quirks specific to 390 (when possible) is a good thing.

Regards,
Halil