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Date: Tue, 16 Jun 2020 14:17:44 +0200
From: Cornelia Huck <cohuck@redhat.com>
Subject: Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without
 IOMMU feature
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To: Halil Pasic <pasic@linux.ibm.com>
Cc: Pierre Morel <pmorel@linux.ibm.com>, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, thomas.lendacky@amd.com, David Gibson <david@gibson.dropbear.id.au>, Ram Pai <linuxram@us.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>

On Tue, 16 Jun 2020 13:57:26 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Tue, 16 Jun 2020 12:52:50 +0200
> Pierre Morel <pmorel@linux.ibm.com> wrote:
> 
> > >>   int virtio_finalize_features(struct virtio_device *dev)
> > >>   {
> > >>   	int ret = dev->config->finalize_features(dev);
> > >> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device *dev)
> > >>   	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
> > >>   		return 0;
> > >>   
> > >> +	if (arch_needs_iommu_platform(dev) &&
> > >> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> > >> +		return -EIO;
> > >> +    
> > > 
> > > Why EIO?    
> > 
> > Because I/O can not occur correctly?
> > I am open to suggestions.  
> 
> We use -ENODEV if feature when the device rejects the features we
> tried to negotiate (see virtio_finalize_features()) and -EINVAL when
> the F_VERSION_1 and the virtio-ccw revision ain't coherent (in
> virtio_ccw_finalize_features()). Any of those seems more fitting
> that EIO to me. BTW does the error code itself matter in any way,
> or is it just OK vs some error?

If I haven't lost my way, we end up in the driver core probe failure
handling; we probably should do -ENODEV if we just want probing to fail
and -EINVAL or -EIO if we want the code to moan.