linux-kernel - Re: [PATCH v5] xen-pciback: allow compiling on other archs than x86

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Date:   Thu, 30 Sep 2021 14:49:38 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     boris.ostrovsky@...cle.com, julien@....org, sstabellini@...nel.org,
        jbeulich@...e.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Anastasiia Lukianenko <anastasiia_lukianenko@...m.com>
Subject: Re: [PATCH v5] xen-pciback: allow compiling on other archs than x86

On 28.09.21 09:35, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> 
> Xen-pciback driver was designed to be built for x86 only. But it
> can also be used by other architectures, e.g. Arm.
> 
> Currently PCI backend implements multiple functionalities at a time,
> such as:
> 1. It is used as a database for assignable PCI devices, e.g. xl
>     pci-assignable-{add|remove|list} manipulates that list. So, whenever
>     the toolstack needs to know which PCI devices can be passed through
>     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 device
>     driver and bound to pciback (strictly speaking it is not required
>     that the device is bound to pciback, but pciback is again used as a
>     database of the passed through PCI devices, so we can re-bind the
>     devices back to their original drivers when guest domain shuts down)
> 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-frontend
> 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.
> 
> For that add new configuration options CONFIG_XEN_PCI_STUB and
> CONFIG_XEN_PCIDEV_STUB, so the driver can be limited in its
> functionality, e.g. no support for para-virtualised scenario.
> x86 platform will continue using CONFIG_XEN_PCIDEV_BACKEND for the
> fully featured backend driver.
> 
> Please note, that CONFIG_XEN_PCIDEV_BACKEND and CONFIG_XEN_PCIDEV_STUB
> are mutually exclusive.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> Signed-off-by: Anastasiia Lukianenko <anastasiia_lukianenko@...m.com>
> Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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