RE: [RFC v1] virtio: add virtio-over-PCI driver

[Zang Roy-R61911]

> -----Original Message-----
> From: Ira Snyder [mailto:iws@xxxxxxxxxxxxxxxx] 
> Sent: Friday, February 20, 2009 0:15 AM
> To: Zang Roy-R61911
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxx; 
> netdev@xxxxxxxxxxxxxxx; Rusty Russell; Arnd Bergmann; 
> Jan-Bernd Themann
> Subject: Re: [RFC v1] virtio: add virtio-over-PCI driver
> 
> On Thu, Feb 19, 2009 at 02:10:08PM +0800, Zang Roy-R61911 wrote:
> >  
> > 
> > > -----Original Message-----
> > > From: 
> > > linuxppc-dev-bounces+tie-fei.zang=freescale.com@xxxxxxxxxx 
> > > [mailto:linuxppc-dev-bounces+tie-fei.zang=freescale.com@ozlabs
> > > .org] On Behalf Of Ira Snyder
> > > Sent: Wednesday, February 18, 2009 6:24 AM
> > > To: linux-kernel@xxxxxxxxxxxxxxx
> > > Cc: linuxppc-dev@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Rusty 
> > > Russell; Arnd Bergmann; Jan-Bernd Themann
> > > Subject: [RFC v1] virtio: add virtio-over-PCI driver
> > snip
> > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > > index 3dd6294..efcf56b 100644
> > > --- a/drivers/virtio/Kconfig
> > > +++ b/drivers/virtio/Kconfig
> > > @@ -33,3 +33,25 @@ config VIRTIO_BALLOON
> > >  
> > >  	 If unsure, say M.
> > >  
> > > +config VIRTIO_OVER_PCI_HOST
> > > +	tristate "Virtio-over-PCI Host support (EXPERIMENTAL)"
> > > +	depends on PCI && EXPERIMENTAL
> > > +	select VIRTIO
> > > +	---help---
> > > +	  This driver provides the host support necessary for 
> > > using virtio
> > > +	  over the PCI bus with a Freescale MPC8349EMDS 
> > > evaluation board.
> > > +
> > > +	  If unsure, say N.
> > > +
> > > +config VIRTIO_OVER_PCI_FSL
> > > +	tristate "Virtio-over-PCI Guest support (EXPERIMENTAL)"
> > > +	depends on MPC834x_MDS && EXPERIMENTAL
> > > +	select VIRTIO
> > > +	select DMA_ENGINE
> > > +	select FSL_DMA
> > > +	---help---
> > > +	  This driver provides the guest support necessary for 
> > > using virtio
> > > +	  over the PCI bus.
> > > +
> > > +	  If unsure, say N.
> > > +
> > > diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> > > index 6738c44..f31afaa 100644
> > > --- a/drivers/virtio/Makefile
> > > +++ b/drivers/virtio/Makefile
> > > @@ -2,3 +2,5 @@ obj-$(CONFIG_VIRTIO) += virtio.o
> > >  obj-$(CONFIG_VIRTIO_RING) += virtio_ring.o
> > >  obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
> > >  obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
> > > +obj-$(CONFIG_VIRTIO_OVER_PCI_HOST) += vop_host.o
> > > +obj-$(CONFIG_VIRTIO_OVER_PCI_FSL) += vop_fsl.o
> > I suppose we  need to build the kernel twice. one for 
> vop_host  (on host
> > with pci enabled) and the
> > other is for vop_fsl ( on agent with pci disabled). Is it 
> possible to
> > build one image for both host and 
> > agent.  We do not scan the pci bus if the controller is 
> configured to
> > agent.
> > 
> 
> You should be able to build a kernel with support for both host and
> guest operation, and then use the device tree to switch which 
> driver you
> get. The host driver won't be used without a PCI bus, and the guest
> driver won't be used without the message unit.
Good.
Is it necssary to commit a extra dts for the agent mode? or just
document it?

> 
> > Also, is it possible to include mpc85xx architecture? They should be
> > same.
> > There is some code for 85xx in Fresscale BSP.
> > 
> http://www.bitshrine.org/gpp/linux-fsl-2.6.23-MPC8568MDS_PCI_A
> gent_PCIe_
> > EP_Drvier.patch
> 
> I looked at the cardnet driver before I implemented my PCINet 
> driver. I
> hunch it would be rejected for the same reasons, but maybe 
> not. 
That is also our concern :-(

>Also, it
> makes no use of DMA, which is critical for good transfer speed. Using
> memcpy() in PCINet gives performance around 10 mbit/sec, which is
> terrible.
I can see your improvement for performance.

> 
> I'm sure the driver isn't very hard to port to 85xx, I just don't have
> any 85xx boards to test with. The driver only directly interacts with
> the messaging unit, which is a pretty simple piece of hardware.
No matter. It is OK to just support 83xx boards currently.
85xx baords can be dealed with later.
Finally, I hope this driver can support 83xx /85xx boards pci and pci
express mode.
Roy
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