linux-kernel - RE: [PATCH 6/6 v3] PCI: document the change

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Date:	Tue, 14 Oct 2008 08:23:34 +0800
From:	"Dong, Eddie" <eddie.dong@...el.com>
To:	"Matthew Wilcox" <matthew@....cx>, "Zhao, Yu" <yu.zhao@...el.com>
Cc:	<linux-pci@...r.kernel.org>,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	"Randy Dunlap" <randy.dunlap@...cle.com>,
	"Grant Grundler" <grundler@...isc-linux.org>,
	"Alex Chiang" <achiang@...com>,
	"Roland Dreier" <rdreier@...co.com>, "Greg KH" <greg@...ah.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<virtualization@...ts.linux-foundation.org>,
	"Dong, Eddie" <eddie.dong@...el.com>
Subject: RE: [PATCH 6/6 v3] PCI: document the change

Matthew Wilcox wrote:
 
> Wouldn't it be more useful to have the iov/N directories
> be a symlink to the actual pci_dev used by the virtual
> function? 

The main concern here is that a VF may be disabed such as when PF enter
D3 state or undergo an reset and thus be plug-off, but user won't
re-configure the VF in case the PF return back to working state.

> 
>> +For network device, there are:
>> +       - /sys/bus/pci/devices/BB:DD.F/iov/N/mac
>> +       - /sys/bus/pci/devices/BB:DD.F/iov/N/vlan
>> +               (value update will notify PF driver)
> 
> We already have tools to set the MAC and VLAN parameters
> for network devices.

Do you mean Ethtool? If yes, it is impossible for SR-IOV since the
configuration has to be done in PF side, rather than VF.

> 
> I'm not 100% convinced about this API.  The assumption
> here is that the driver will do it, but I think it should
> probably be in the core.  The driver probably wants to be

Our concern is that the PF driver may put an default state when it is
loaded so that SR-IOV can work without any user level configuration, but
of course the driver won't dynamically change it.
Do u mean we remove this ability?

> notified that the PCI core is going to create a virtual
> function, and would it please prepare to do so, but I'm
> not convinced this should be triggered by the driver. 
> How would the driver decide to create a new virtual
> function?  
> 
> 
> From my reading of the SR-IOV spec, this isn't how it's
> supposed to work.  The device is supposed to be a fully
> functional PCI device that on demand can start peeling
> off virtual functions; it's not supposed to boot up and
> initialise all its virtual functions at once. 

The spec defines either we enable all VFs or Disable. Per VF enabling is
not supported.
Is this what you concern?

Thanks, eddie
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