[PATCH V2] amd iommu: re-enable iommu msi if dom0 disabled it

[Wei Wang <wei.wang2@amd.com>]

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Hi Jan & Andrew

I had attached a revised patch, please check it.

I found that the following Linux commit triggers this issue. It has been 
included into 3.4 pv_ops.

" commit a776c491ca5e38c26d9f66923ff574d041e747f4
   Author: Eric W. Biederman <ebiederm@xmission.com>
   Date:   Mon Oct 17 11:46:06 2011 -0700

   PCI: msi: Disable msi interrupts when we initialize a pci device "

Thanks,
Wei

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# HG changeset patch
# Parent f6bfaf9daa508c31b2bca0e461202db2759426fc
# User Wei Wang <wei.wang2@amd.com>
Re-enable iommu msi capability block if it is disabled by dom0
Linux commit a776c491ca5e38c26d9f66923ff574d041e747f4 disables msi interrupts. If is
running as a dom0, iommu interrupt will be disabled and hypervisor cannot process any
event and ppr logs afterwards.

Signed-off-by: Wei Wang <wei.wang2@amd.com>

diff -r f6bfaf9daa50 xen/drivers/passthrough/amd/pci_amd_iommu.c
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c	Wed Jun 06 16:37:05 2012 +0100
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c	Tue Jun 12 13:58:40 2012 +0200
@@ -81,6 +81,30 @@ static void disable_translation(u32 *dte
     dte[0] = entry;
 }
 
+static void iommu_msi_check_enable(struct amd_iommu *iommu)
+{
+    unsigned long flags;
+    uint16_t control;
+    uint8_t bus = PCI_BUS(iommu->bdf);
+    uint8_t dev = PCI_SLOT(iommu->bdf);
+    uint8_t func = PCI_FUNC(iommu->bdf);
+
+    ASSERT( iommu->msi_cap );
+
+    spin_lock_irqsave(&iommu->lock, flags);
+
+    control = pci_conf_read16(iommu->seg, bus, dev, func,
+                              iommu->msi_cap + PCI_MSI_FLAGS);
+    if ( !(control & PCI_MSI_FLAGS_ENABLE) )
+    {    
+        control |= PCI_MSI_FLAGS_ENABLE;
+        pci_conf_write16(iommu->seg, bus, dev, func,
+                         iommu->msi_cap + PCI_MSI_FLAGS, control);
+    }
+
+    spin_unlock_irqrestore(&iommu->lock, flags);
+}
+
 static void amd_iommu_setup_domain_device(
     struct domain *domain, struct amd_iommu *iommu, int bdf)
 {
@@ -101,6 +125,12 @@ static void amd_iommu_setup_domain_devic
     if ( ats_enabled )
         dte_i = 1;
 
+    /* 
+     * In some cases, dom0 disables iommu msi capability, 
+     * check and re-enable it here.
+     */
+    iommu_msi_check_enable(iommu); 
+
     /* get device-table entry */
     req_id = get_dma_requestor_id(iommu->seg, bdf);
     dte = iommu->dev_table.buffer + (req_id * IOMMU_DEV_TABLE_ENTRY_SIZE);

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