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

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

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

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;
+
        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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