linux-kernel - Re: [PATCH] uio/uio_pci_generic: Add SR-IOV support

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Date:   Thu, 28 Sep 2017 14:46:09 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Don Dutile <ddutile@...hat.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        "Bryant G. Ly" <bryantly@...ux.vnet.ibm.com>,
        Bodong Wang <bodong@...lanox.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH] uio/uio_pci_generic: Add SR-IOV support

On Thu, 2017-09-28 at 08:22 -0400, Don Dutile wrote:
> 
> After reading Alex's response, I now understand Dave's question
> better and why the patch won't work in general.

UIO doesn't work "in general". It requires a very *specific* userspace
driver for the hardware in question, which needs to know what it's
doing.

> In every SRIOV capable device I've run into to date, the PF has
> to know the VFs are being assigned due to some resource mgmt, if not
> internal (e.g., switch) configuration reasons.
> The reasons are often subtle.

Sure. If there's actually a userspace driver (which in my case there
isn't), and if that's needed for the hardware ins question (which in my
case it isn't), then it'd need to do that before enabling the VFs via
the user-level sysfs interface of which you speak.

>  From the context of the patches (uio), why aren't VFs enabled via
> user-level sysfs interface? That was provided for user-mgmt apps
> to have a PCIe-generic/common, device-independent method of VF
> enablement 

That is *precisely* what we're doing. But the user-space sysfs
interface doesn't actually *exist* unless a driver is bound to the
device in question, with a .sriov-configure method. Which is where I
came in... :)

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