linux-kernel - Re: [Question] Is it must for vfio-mdev parent driver to implement a pci-compliant configuration r/w interface

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Date: Tue, 2 Jan 2024 12:28:22 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: Wu Zongyong <wuzongyong@...ux.alibaba.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 wutu.xq2@...ux.alibaba.com
Subject: Re: [Question] Is it must for vfio-mdev parent driver to implement
 a pci-compliant configuration r/w interface

On Tue, 26 Dec 2023 10:30:04 +0800
Wu Zongyong <wuzongyong@...ux.alibaba.com> wrote:

> Hi,
> 
> For vfio, I know there are two method to get region size:
>   1. VFIO_DEVICE_GET_REGION_INFO ioctl
>   2. write a value of all 1's to the bar register of vfio-device fd
>     and then read the value back which is described in pci spec
> 
> Now I am curious about is it a must for a vfio-mdev parent driver to
> implement the method 2? Or it is just a optional interface.

If there's not a working, compliant config space, the device shouldn't
claim to implement a vfio-pci interface.  There's vfio-platform
available for non-PCI devices.  While the BAR size may be found via
either REGION_INFO or config space itself, the BAR address space is
only found via config space, ie. memory or IO, 32 or 64-bit,
prefetchable or not.  Thanks,

Alex