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From: Cornelia Huck <cohuck@redhat.com>
To: Matthew Rosato <mjrosato@linux.ibm.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	schnelle@linux.ibm.com, pmorel@linux.ibm.com,
	borntraeger@de.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com,
	gerald.schaefer@linux.ibm.com, linux-s390@vger.kernel.org,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/5] vfio-pci/zdev: define the vfio_zdev header
Date: Mon, 5 Oct 2020 18:28:11 +0200	[thread overview]
Message-ID: <20201005182811.6c17ed6b.cohuck@redhat.com> (raw)
In-Reply-To: <e0688173-8c5a-1797-8398-235c5e406bc1@linux.ibm.com>

On Mon, 5 Oct 2020 12:16:10 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> On 10/5/20 12:01 PM, Cornelia Huck wrote:
> > On Mon, 5 Oct 2020 09:52:25 -0400
> > Matthew Rosato <mjrosato@linux.ibm.com> wrote:
> >   
> >> On 10/2/20 5:44 PM, Alex Williamson wrote:  
> >   
> >>> Can you discuss why a region with embedded capability chain is a better
> >>> solution than extending the VFIO_DEVICE_GET_INFO ioctl to support a
> >>> capability chain and providing this info there?  This all appears to be
> >>> read-only info, so what's the benefit of duplicating yet another  
> >>
> >> It is indeed read-only info, and the device region was defined as such.
> >>
> >> I would not necessarily be opposed to extending VFIO_DEVICE_GET_INFO
> >> with these defined as capabilities; I'd say a primary motivating factor
> >> to putting these in their own region was to avoid stuffing a bunch of
> >> s390-specific capabilities into a general-purpose ioctl response.  
> > 
> > Can't you make the zdev code register the capabilities? That would put
> > them nicely into their own configurable part.
> >   
> 
> I can still keep the code that adds these capabilities in the zdev .c 
> file, thus meaning they will only be added for s390 zpci devices -- but 
> the actual definition of them should probably instead be in vfio.h, no? 
> (maybe that's what you mean, but let's lay it out just in case)
> 
> The capability IDs would be shared with any other potential user of 
> VFIO_DEVICE_GET_INFO (I guess there is precedent for this already, 
> nvlink2 does this for vfio_region_info, see 
> VFIO_REGION_INFO_CAP_NVLINK2_SSATGT as an example).
> 
> Today, ZPCI would be the only users of VFIO_DEVICE_GET_INFO capability 
> chains.  Tomorrow, some other type might use them too.  Unless we want 
> to put a stake in the ground that says there will never be a case for a 
> capability that all devices share on VFIO_DEVICE_GET_INFO, I think we 
> should keep the IDs unique and define the capabilities in vfio.h but do 
> the corresponding add_capability() calls from a zdev-specific file.

Agreed. We should have enough space for multiple users, and I do not
consider reserving the IDs cluttering.


  reply	other threads:[~2020-10-05 16:28 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-02 20:00 [PATCH v2 0/5] Pass zPCI hardware information via VFIO Matthew Rosato
2020-10-02 20:00 ` [PATCH v2 1/5] s390/pci: stash version in the zpci_dev Matthew Rosato
2020-10-02 20:00 ` [PATCH v2 2/5] s390/pci: track whether util_str is valid " Matthew Rosato
2020-10-06 15:24   ` Cornelia Huck
2020-10-02 20:00 ` [PATCH v2 3/5] vfio-pci/zdev: define the vfio_zdev header Matthew Rosato
2020-10-02 21:44   ` Alex Williamson
2020-10-05 13:52     ` Matthew Rosato
2020-10-05 16:01       ` Cornelia Huck
2020-10-05 16:16         ` Matthew Rosato
2020-10-05 16:28           ` Cornelia Huck [this message]
2020-10-02 20:00 ` [PATCH v2 4/5] vfio-pci/zdev: use a device region to retrieve zPCI information Matthew Rosato
2020-10-02 20:00 ` [PATCH v2 5/5] MAINTAINERS: Add entry for s390 vfio-pci Matthew Rosato
2020-10-06 15:27   ` Cornelia Huck
2020-10-02 20:18 ` [PATCH v2 0/5] Pass zPCI hardware information via VFIO Matthew Rosato

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