linux-kernel - Re: [PATCH 4/4 v2] PCI: document the change

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Date:	Mon, 1 Sep 2008 09:42:17 -0600
From:	Alex Chiang <achiang@...com>
To:	"Zhao, Yu" <yu.zhao@...el.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>, linux-pci@...r.kernel.org,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Greg KH <greg@...ah.com>,
	Grant Grundler <grundler@...isc-linux.org>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xensource.com
Subject: Re: [PATCH 4/4 v2] PCI: document the change

* Zhao, Yu <yu.zhao@...el.com>:
> +1. Overview
> +
> +1.1 What is SR-IOV
> +
> +Single Root I/O Virtualization (SR-IOV) is a PCI Express Extended
> +capability which makes one physical device appear as multiple virtual
> +devices. The physical device is referred to as Physical Function while
> +the virtual devices are referred to as Virtual Functions. Allocation
> +of Virtual Functions can be dynamically controlled by Physical Function
> +via registers encapsulated in the capability. By default, this feature
> +is not enabled and the Physical Function behaves as traditional PCIe
> +device. Once it's turned on, each Virtual Function's PCI configuration
> +space can be accessed by its own Bus, Device and Function Number (Routing
> +ID). And each Virtual Function also has PCI Memory Space, which is used
> +to map its register set. Virtual Function device driver operates on the
> +register set so it can be functional and appear as a real existing PCI
> +device.
> +
> +1.2 What is ARI
> +
> +Alternative Routing-ID Interpretation (ARI) allows a PCI Express Endpoint
> +to use its device number field as part of function number. Traditionally,
> +an Endpoint can only have 8 functions, and the device number of all
> +Endpoints is zero. With ARI enabled, an Endpoint can have up to 256
> +functions by using device number in conjunction with function number to
> +indicate a function in the device. This is almost transparent to the Linux
> +kernel because the Linux kernel still can use 8-bit bus number field plus
> +8-bit devfn number field to locate a function. ARI is managed via the ARI
> +Forwarding bit in the Device Capabilities 2 register of the PCI Express
> +Capability on the Root Port or the Downstream Port and a new ARI Capability
> +on the Endpoint.
> +
> +
> +2. User Guide
> +
> +2.1 How can I manage SR-IOV
> +
> +If a device supports SR-IOV, then there should be some entires under
                                                          entries
> +/sys/bus/pci/slots/. The names of the entires are XXXX:BB:DD.F-iov-NNNN,
                                         entries
> +where the first part (XXXX:BB:DD.F) is the domain, bus, device and function
> +number of the device, and the third part (NNNN) is the index of a Virtual
> +Function. There are three files under the entry: power, param and address.

So are you saying here that you will actually create sysfs files
named:

	/sys/bus/pci/slots/XXXX:BB:DD.F-iov-NNNN

We just spent some effort cleaning out this directory and getting
human-readable names in /sys/bus/pci/slots/. The entries created
there _should_ match the labelling on the physical chassis,
assuming firmware tells us the right name.

How will these particular slot entries be created? Do the
individual hotplug drivers create them?

Sorry, I guess I haven't read the patch series, just skimmed the
documentation. I can go do that before asking any further dumb
questions, but this little bit of information was a bit
surprising to me.

> +	- Writing 1 to the "power" will enable the Virtual Function,
> +	and 0 will disable the Virtual Function; Reading it will get
> +	status of the Virtual Function.
> +	- Reading the "address" will get the bus, device and function
> +	number of the Virtual Function.
> +	- The "param" is the device specific parameters which may be
> +	used by the Physical or Virtual Functions drivers.
> +
> +2.2 How can I use Virtual Functions
> +
> +Virtual Functions is treated as hot-plugged PCI devices in the kernel,
> +so they should be able to work in the same way as real PCI devices.
> +NOTE: Virtual Function device driver must be loaded to make it work.

Ok, I'll go read the rest of the patch series; looks like you
wrote a new virtual function driver.

Thanks.

/ac

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