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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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@intel.com>
> 
> 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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