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

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

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)?

> 
> >   
> >> 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.

Regards,
Halil

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