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Subject: Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV
To:     Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>,
        Jan Beulich <jbeulich@suse.com>,
        Oleksandr Andrushchenko <andr2000@gmail.com>
Cc:     "boris.ostrovsky@oracle.com" <boris.ostrovsky@oracle.com>,
        "julien@xen.org" <julien@xen.org>,
        "sstabellini@kernel.org" <sstabellini@kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20210927065822.350973-1-andr2000@gmail.com>
 <e472468a-625e-6c4d-a9c2-85594e2ff908@suse.com>
 <accd0220-a9d7-145b-6632-9dee085ffc65@epam.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <1cf5fbf3-6453-e258-3940-8b5bb96117b6@suse.com>
Date:   Mon, 27 Sep 2021 09:54:24 +0200
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From: Juergen Gross <jgross@suse.com>
To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>,
 Jan Beulich <jbeulich@suse.com>, Oleksandr Andrushchenko <andr2000@gmail.com>
Cc: "boris.ostrovsky@oracle.com" <boris.ostrovsky@oracle.com>,
 "julien@xen.org" <julien@xen.org>,
 "sstabellini@kernel.org" <sstabellini@kernel.org>,
 "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Message-ID: <1cf5fbf3-6453-e258-3940-8b5bb96117b6@suse.com>
Subject: Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV
References: <20210927065822.350973-1-andr2000@gmail.com>
 <e472468a-625e-6c4d-a9c2-85594e2ff908@suse.com>
 <accd0220-a9d7-145b-6632-9dee085ffc65@epam.com>
In-Reply-To: <accd0220-a9d7-145b-6632-9dee085ffc65@epam.com>

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On 27.09.21 09:35, Oleksandr Andrushchenko wrote:
>=20
> On 27.09.21 10:26, Jan Beulich wrote:
>> On 27.09.2021 08:58, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>
>>> Currently PCI backend implements multiple functionalities at a time.
>>> To name a few:
>>> 1. It is used as a database for assignable PCI devices, e.g. xl
>>>      pci-assignable-{add|remove|list} manipulates that list. So, when=
ever
>>>      the toolstack needs to know which PCI devices can be passed thro=
ugh
>>>      it reads that from the relevant sysfs entries of the pciback.
>>> 2. It is used to hold the unbound PCI devices list, e.g. when passing=

>>>      through a PCI device it needs to be unbound from the relevant de=
vice
>>>      driver and bound to pciback (strictly speaking it is not require=
d
>>>      that the device is bound to pciback, but pciback is again used a=
s a
>>>      database of the passed through PCI devices, so we can re-bind th=
e
>>>      devices back to their original drivers when guest domain shuts d=
own)
>>> 3. Device reset for the devices being passed through
>>> 4. Para-virtualised use-cases support
>>>
>>> The para-virtualised part of the driver is not always needed as some
>>> architectures, e.g. Arm or x86 PVH Dom0, are not using backend-fronte=
nd
>>> model for PCI device passthrough. For such use-cases make the very
>>> first step in splitting the xen-pciback driver into two parts: Xen
>>> PCI stub and PCI PV backend drivers.
>>>
>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.=
com>
>>>
>>> ---
>>> Changes since v3:
>>> - Move CONFIG_XEN_PCIDEV_STUB to the second patch
>> I'm afraid this wasn't fully done:
>>
>>> --- a/drivers/xen/xen-pciback/Makefile
>>> +++ b/drivers/xen/xen-pciback/Makefile
>>> @@ -1,5 +1,6 @@
>>>    # SPDX-License-Identifier: GPL-2.0
>>>    obj-$(CONFIG_XEN_PCIDEV_BACKEND) +=3D xen-pciback.o
>>> +obj-$(CONFIG_XEN_PCIDEV_STUB) +=3D xen-pciback.o
>> While benign when added here, this addition still doesn't seem to
>> belong here.
>=20
> My bad. So, it seems without CONFIG_XEN_PCIDEV_STUB the change seems
>=20
> to be non-functional. With CONFIG_XEN_PCIDEV_STUB we fail to build on 3=
2-bit
>=20
> architectures...
>=20
> What would be the preference here? Stefano suggested that we still defi=
ne
>=20
> CONFIG_XEN_PCIDEV_STUB, but in disabled state, e.g. we add tristate to =
it
>=20
> in the second patch
>=20
> Another option is just to squash the two patches.

Squashing would be fine for me.


Juergen

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