[PATCH v6 2/4] x86/msi: rearrange read_pci_mem_bar slightly

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

Use pdev->sbdf instead of the PCI_SBDF macro in calls to pci_* functions
where appropriate. Move NULL check earlier.

Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v5->v6:
* no change

v4->v5:
* add Jan's R-b

v3->v4:
* new patch

Suggested-by tag added based on conversation at [1]

[1] https://lists.xenproject.org/archives/html/xen-devel/2023-08/msg01886.html
---
 xen/arch/x86/msi.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/xen/arch/x86/msi.c b/xen/arch/x86/msi.c
index 8d4fd43b10a6..a78367d7cf5d 100644
--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -674,19 +674,19 @@ static u64 read_pci_mem_bar(u16 seg, u8 bus, u8 slot, u8 
func, u8 bir, int vf)
     {
         struct pci_dev *pdev = pci_get_pdev(NULL,
                                             PCI_SBDF(seg, bus, slot, func));
-        unsigned int pos = pci_find_ext_capability(PCI_SBDF(seg, bus, slot,
-                                                            func),
-                                                   PCI_EXT_CAP_ID_SRIOV);
-        uint16_t ctrl = pci_conf_read16(PCI_SBDF(seg, bus, slot, func),
-                                        pos + PCI_SRIOV_CTRL);
-        uint16_t num_vf = pci_conf_read16(PCI_SBDF(seg, bus, slot, func),
-                                          pos + PCI_SRIOV_NUM_VF);
-        uint16_t offset = pci_conf_read16(PCI_SBDF(seg, bus, slot, func),
-                                          pos + PCI_SRIOV_VF_OFFSET);
-        uint16_t stride = pci_conf_read16(PCI_SBDF(seg, bus, slot, func),
-                                          pos + PCI_SRIOV_VF_STRIDE);
-
-        if ( !pdev || !pos ||
+        unsigned int pos;
+        uint16_t ctrl, num_vf, offset, stride;
+
+        if ( !pdev )
+            return 0;
+
+        pos = pci_find_ext_capability(pdev->sbdf, PCI_EXT_CAP_ID_SRIOV);
+        ctrl = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_CTRL);
+        num_vf = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_NUM_VF);
+        offset = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_VF_OFFSET);
+        stride = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_VF_STRIDE);
+
+        if ( !pos ||
              !(ctrl & PCI_SRIOV_CTRL_VFE) ||
              !(ctrl & PCI_SRIOV_CTRL_MSE) ||
              !num_vf || !offset || (num_vf > 1 && !stride) ||
-- 
2.42.0