RE: [RFC v2 1/4] hisi-acc-vfio-pci: add new vfio_pci driver for HiSilicon ACC devices

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Max Gurtovoy [mailto:mgurtovoy@nvidia.com]
> Sent: 05 July 2021 10:42
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> Leon Romanovsky <leon@kernel.org>
> Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-crypto@vger.kernel.org; alex.williamson@redhat.com; jgg@nvidia.com;
> Linuxarm <linuxarm@huawei.com>; liulongfang <liulongfang@huawei.com>;
> Zengtao (B) <prime.zeng@hisilicon.com>; yuzenghui
> <yuzenghui@huawei.com>; Jonathan Cameron
> <jonathan.cameron@huawei.com>; Wangzhou (B) <wangzhou1@hisilicon.com>
> Subject: Re: [RFC v2 1/4] hisi-acc-vfio-pci: add new vfio_pci driver for HiSilicon
> ACC devices
> 
> 
> On 7/5/2021 11:47 AM, Shameerali Kolothum Thodi wrote:
> >
> >> -----Original Message-----
> >> From: Leon Romanovsky [mailto:leon@kernel.org]
> >> Sent: 04 July 2021 08:04
> >> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
> >> Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org;
> >> linux-crypto@vger.kernel.org; alex.williamson@redhat.com;
> jgg@nvidia.com;
> >> mgurtovoy@nvidia.com; Linuxarm <linuxarm@huawei.com>; liulongfang
> >> <liulongfang@huawei.com>; Zengtao (B) <prime.zeng@hisilicon.com>;
> >> yuzenghui <yuzenghui@huawei.com>; Jonathan Cameron
> >> <jonathan.cameron@huawei.com>; Wangzhou (B)
> <wangzhou1@hisilicon.com>
> >> Subject: Re: [RFC v2 1/4] hisi-acc-vfio-pci: add new vfio_pci driver for
> HiSilicon
> >> ACC devices
> >>
> >> On Fri, Jul 02, 2021 at 10:58:46AM +0100, Shameer Kolothum wrote:
> >>> Add a vendor-specific vfio_pci driver for HiSilicon ACC devices.
> >>> This will be extended in follow-up patches to add support for
> >>> vfio live migration feature.
> >>>
> >>> Signed-off-by: Shameer Kolothum
> >> <shameerali.kolothum.thodi@huawei.com>
> >>> ---
> >>>   drivers/vfio/pci/Kconfig             |   9 +++
> >>>   drivers/vfio/pci/Makefile            |   2 +
> >>>   drivers/vfio/pci/hisi_acc_vfio_pci.c | 100
> +++++++++++++++++++++++++++
> >>>   3 files changed, 111 insertions(+)
> >>>   create mode 100644 drivers/vfio/pci/hisi_acc_vfio_pci.c
> >> <...>
> >>
> >>> +static const struct vfio_device_ops hisi_acc_vfio_pci_ops = {
> >>> +	.name		= "hisi-acc-vfio-pci",
> >>> +	.open		= hisi_acc_vfio_pci_open,
> >>> +	.release	= vfio_pci_core_release,
> >>> +	.ioctl		= vfio_pci_core_ioctl,
> >>> +	.read		= vfio_pci_core_read,
> >>> +	.write		= vfio_pci_core_write,
> >>> +	.mmap		= vfio_pci_core_mmap,
> >>> +	.request	= vfio_pci_core_request,
> >>> +	.match		= vfio_pci_core_match,
> >>> +	.reflck_attach	= vfio_pci_core_reflck_attach,
> >> I don't remember what was proposed in vfio-pci-core conversion patches,
> >> but would expect that default behaviour is to fallback to vfio_pci_core_*
> API
> >> if ".release/.ioctl/e.t.c" are not redefined.
> > Yes, that would be nice, but don't think it does that in latest(v4).
> >
> > Hi Max,
> > Could we please consider fall back to the core defaults, may be check and
> assign defaults
> > in vfio_pci_core_register_device() ?
> 
> I don't see why we should do this.
> 
> vfio_pci_core.ko is just a library driver. It shouldn't decide for the
> vendor driver ops.
> 
> If a vendor driver would like to use its helper functions - great.
> 
> If it wants to override it - great.
> 
> If it wants to leave some op as NULL - it can do it also.

Based on the documentation of the vfio_device_ops callbacks,
It looks like we already have a precedence in the case of reflck_attach
callback where it uses the vfio core default one, if it is not implemented.

Also I would imagine that in majority use cases the vendor drivers will be
defaulting to core functions. 

I think, in any case, it would be good to update the Documentation based on
which way we end up doing this.

Thanks,
Shameer 

 
> 
> 
> >
> > Thanks,
> > Shameer