linux-kernel - Re: [RFC 0/1] New PCI Switch Management Driver

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Message-ID: <20161219172903.GB1043@localhost.localdomain>
Date:   Mon, 19 Dec 2016 12:29:03 -0500
From:   Keith Busch <keith.busch@...el.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Myron Stowe <myron.stowe@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Jonathan Corbet <corbet@....net>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        Stephen Bates <stephen.bates@...rosemi.com>,
        linux-pci <linux-pci@...r.kernel.org>, linux-doc@...r.kernel.org,
        linux-nvme@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/1] New PCI Switch Management Driver

On Mon, Dec 19, 2016 at 10:06:56AM -0700, Logan Gunthorpe wrote:
> As I noted, the hardware is compliant and works perfectly fine with the
> in-kernel driver. However, the hardware has many additional custom
> features that are not covered by the PCI specs. For example, it has an
> interface to count packets that match a specific criteria. It also has
> firmware that can be expanded to do completely custom things by the
> user. Additionally, the switch is _very_ configurable and has a
> configuration file that can be uploaded and downloaded.
> 
> All these features and more are exposed through a special management
> endpoint that is completely separate from the standard PCI switch
> interface. This work is a driver for that endpoint and is not required
> to use the switch. It only makes the advanced features available to the
> user.

Since the in-kernel driver binds to the device, won't this driver
conflict with the initialization the in-kernel one already does? Bus
master, MSI setup, etc?

Could you also provide the reasoning against making the functionality
this driver provides in user space?