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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.04.12 at 17:25, "Hao, Xudong" <xudong.hao@xxxxxxxxx> 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.
> 
> 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 19834d1..82aac5b 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -334,6 +334,14 @@ static int __devinit pcistub_init_device(struct pci_dev 
> *dev)
>       dev_dbg(&dev->dev, "reset device\n");
>       xen_pcibk_reset_device(dev);
>  
> +     /* set default value */
> +     unsigned long type = PCI_EXP_OBFF_SIGNAL_ALWAYS;
> +     int snoop_lat_ns = 1024, nosnoop_lat_ns = 1024; /* 1024ns is max value 
> */
> +
> +     /* 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. 
> +      */
> +     pci_enable_ltr(dev);
> +     pci_set_ltr(dev, snoop_lat_ns, nosnoop_lat_ns);

Wouldn't the guest kernel be able to do this itself, as it's just playing
with bits in the PCIE capability structure, or the LTR extended one?

If not, shouldn't you properly report (or at least log) errors here?

> +
> +     /* 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.
> +      */
> +     pci_enable_obff(dev, type);

Similarly here.

Jan

> +
>       dev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
>       return 0;
> 
> 
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