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

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 19 Jan 2021 12:47:24 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Thu, 14 Jan 2021 14:03:25 +0100
> Boris Fiuczynski <fiuczy@linux.ibm.com> wrote:
> 
> > On 12/21/20 5:51 PM, Halil Pasic wrote:  
> > > 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.    
> > 
> > Yesterday I used driverctl successfully for a subchannel on F33.
> > 
> > Not sure what went wrong a couple of months ago but I cannot reproduce 
> > driverctl not working now.  
> 
> Thanks Boris!
> 
> @Conny: IMHO driver_override has to work without this patch. Can you
> figure out, why did you claim it does not (and provide instructions
> on how to reproduce the problem)?

This may have been due to other reasons and only looking like a uevent
issue at the first glance; however, I do not have that particular setup
anymore, so I guess we'll never know.

> 
> >   
> > >     
> > >> 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 totally agree with this.  
> 
> @Vineeth: I think the best way to move forward is to respin this patch
> with a commit message, that doesn't argue about driver_override.

That sounds good to me.