[PATCH v2] xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
the table is filled. Then it disables INTx just before clearing MASKALL
bit. Currently this approach is rejected by xen-pciback.
According to the PCIe spec, device cannot use INTx when MSI/MSI-X is
enabled. Change the logic to consider INTx disabled if MSI/MSI-X is
enabled. This applies to two places: checking currently enabled
interrupts type, and transition to MSI/MSI-X - where INTx would be
implicitly disabled.

Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
 drivers/xen/xen-pciback/conf_space.c          | 19 +++++++++++++------
 .../xen/xen-pciback/conf_space_capability.c   |  3 ++-
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/xen/xen-pciback/conf_space.c b/drivers/xen/xen-pciback/conf_space.c
index 059de92aea7d..d47eee6c5143 100644
--- a/drivers/xen/xen-pciback/conf_space.c
+++ b/drivers/xen/xen-pciback/conf_space.c
@@ -288,12 +288,6 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
 	u16 val;
 	int ret = 0;
 
-	err = pci_read_config_word(dev, PCI_COMMAND, &val);
-	if (err)
-		return err;
-	if (!(val & PCI_COMMAND_INTX_DISABLE))
-		ret |= INTERRUPT_TYPE_INTX;
-
 	/*
 	 * Do not trust dev->msi(x)_enabled here, as enabling could be done
 	 * bypassing the pci_*msi* functions, by the qemu.
@@ -316,6 +310,19 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
 		if (val & PCI_MSIX_FLAGS_ENABLE)
 			ret |= INTERRUPT_TYPE_MSIX;
 	}
+
+	/*
+	 * PCIe spec says device cannot use INTx if MSI/MSI-X is enabled,
+	 * so check for INTx only when both are disabled.
+	 */
+	if (!ret) {
+		err = pci_read_config_word(dev, PCI_COMMAND, &val);
+		if (err)
+			return err;
+		if (!(val & PCI_COMMAND_INTX_DISABLE))
+			ret |= INTERRUPT_TYPE_INTX;
+	}
+
 	return ret ?: INTERRUPT_TYPE_NONE;
 }
 
diff --git a/drivers/xen/xen-pciback/conf_space_capability.c b/drivers/xen/xen-pciback/conf_space_capability.c
index 097316a74126..eb4c1af44f5c 100644
--- a/drivers/xen/xen-pciback/conf_space_capability.c
+++ b/drivers/xen/xen-pciback/conf_space_capability.c
@@ -236,10 +236,11 @@ static int msi_msix_flags_write(struct pci_dev *dev, int offset, u16 new_value,
 		return PCIBIOS_SET_FAILED;
 
 	if (new_value & field_config->enable_bit) {
-		/* don't allow enabling together with other interrupt types */
+		/* don't allow enabling together with other interrupt type */
 		int int_type = xen_pcibk_get_interrupt_type(dev);
 
 		if (int_type == INTERRUPT_TYPE_NONE ||
+		    int_type == INTERRUPT_TYPE_INTX ||
 		    int_type == field_config->int_type)
 			goto write;
 		return PCIBIOS_SET_FAILED;
-- 
2.37.3