linux-kernel - Re: [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH

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Message-ID: <20180430173028.0dca976c.cohuck@redhat.com>
Date:   Mon, 30 Apr 2018 17:30:28 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:     pasic@...ux.vnet.ibm.com, bjsdjshi@...ux.vnet.ibm.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH_REQ
 event

On Wed, 25 Apr 2018 15:52:19 +0200
Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:

> On 25/04/2018 10:41, Cornelia Huck wrote:
> > On Thu, 19 Apr 2018 16:48:07 +0200
> > Pierre Morel<pmorel@...ux.vnet.ibm.com>  wrote:

> >> diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
> >> index 3284e64..93aab87 100644
> >> --- a/drivers/s390/cio/vfio_ccw_private.h
> >> +++ b/drivers/s390/cio/vfio_ccw_private.h
> >> @@ -76,7 +76,7 @@ enum vfio_ccw_state {
> >>    */
> >>   enum vfio_ccw_event {
> >>   	VFIO_CCW_EVENT_NOT_OPER,
> >> -	VFIO_CCW_EVENT_IO_REQ,
> >> +	VFIO_CCW_EVENT_SSCH_REQ,
> >>   	VFIO_CCW_EVENT_INTERRUPT,
> >>   	VFIO_CCW_EVENT_SCH_EVENT,
> >>   	/* last element! */  
> > I don't think we should separate the ssch handling. The major 
> > difference to halt/clear is that it needs channel program translation. 
> > Everything else (issuing the instruction and processing the interrupt) 
> > are basically the same. If we just throw everything at the hardware 
> > and let the host's channel subsystem figure it out, we already should 
> > be fine with regard to most of the races.  
> 
> We must test at a moment or another the kind of request we do,
> cancel, halt and clear only need the subchannel id in register 1 and as 
> you said are much more direct to implement.
> 
> If we do not separate them here, we need a switch in the "do_io_request" 
> function.
> Is it what you mean?

Yes. Most of the handling should be the same for any function.