Re: [Xen-devel] [PATCH v2] Re-enable LTR/OBFF when device is owned by pciback

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, May 04, 2012 at 07:49:21AM +0000, Hao, Xudong wrote:
> When PCIE device which has LTR/OBFF capabilities is owned by pciback, 
> LTR/OBFF feature may be disabled. This patch re-enable LTR and OBFF, so that 
> guest with device assigned can be benefitted.
> 
> Changes from v1:
> - put the variable definition at the start of function
> - add error log report
> 

Don't you need to disable this when the device is un-assigned from the guest?

> Signed-off-by: Xudong Hao <xudong.hao@xxxxxxxxx>
> 
> diff --git a/drivers/xen/xen-pciback/pci_stub.c 
> b/drivers/xen/xen-pciback/pci_stub.c
> index 097e536..74fbf23 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -313,6 +313,10 @@ static int __devinit pcistub_init_device(struct pci_dev 
> *dev)
>       struct xen_pcibk_dev_data *dev_data;
>       int err = 0;
>  
> +     /* set default value */
> +     unsigned long type = PCI_EXP_OBFF_SIGNAL_ALWAYS;
> +     int snoop_lat_ns = 1024, nosnoop_lat_ns = 1024;

Why these values? Is there a way to fetch optimal values?
> +
>       dev_dbg(&dev->dev, "initializing...\n");
>  
>       /* The PCI backend is not intended to be a module (or to work with
> @@ -369,6 +373,28 @@ static int __devinit pcistub_init_device(struct pci_dev 
> *dev)
>       dev_dbg(&dev->dev, "reset device\n");
>       xen_pcibk_reset_device(dev);
>  
> +     /* Enable LTR and OBFF before do device assignment */
> +     /* LTR(Latency tolerance reporting) allows devices to send
> +      * messages to the root complex indicating their latency tolerance
> +      * for snooped & unsnooped memory transactions.
> +      */
> +     err = pci_enable_ltr(dev);
> +     if (err)
> +             dev_err(&dev->dev, "Counld not enalbe LTR for device!\n");
> +
> +     err = pci_set_ltr(dev, snoop_lat_ns, nosnoop_lat_ns);
> +     if (err)
> +             dev_err(&dev->dev, "Set LTR latency values failed.\n");
> +
> +     /* OBFF (optimized buffer flush/fill), where supported, can help
> +      * improve energy efficiency by giving devices information about
> +      * when interrupts and other activity will have a reduced power
> +      * impact.
> +      */
> +     err = pci_enable_obff(dev, type);
> +     if (err)
> +             dev_err(&dev->dev, "Counld not enalbe OBFF for device!\n");
> +
>       dev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
>       return 0;
> 
> 
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