[dpdk-kmods] linux/igb_uio: fix build for switch fall through

[Ferruh Yigit <ferruh.yigit@intel.com>]

Linux is using '-Wimplicit-fallthrough=5' compiler option, which doesn't
take any fall through comments into account but only uses compiler
'fallthrough' attribute to document fall through action is intended.

"falls through" comment was used in the code which is causing a build
error now, this patch converts comment to the 'fallthrough' macro
defined in the Linux.

To cover the case where Linux version doesn't have the macro, defined it
in the compatibility header too.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
---
 linux/igb_uio/compat.h  | 4 ++++
 linux/igb_uio/igb_uio.c | 6 +++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/linux/igb_uio/compat.h b/linux/igb_uio/compat.h
index 8dbb896ae118..04ff7f60031f 100644
--- a/linux/igb_uio/compat.h
+++ b/linux/igb_uio/compat.h
@@ -152,3 +152,7 @@ static inline bool igbuio_kernel_is_locked_down(void)
 	return false;
 #endif
 }
+
+#ifndef fallthrough
+#define fallthrough	do {} while (0)  /* fallthrough */
+#endif
diff --git a/linux/igb_uio/igb_uio.c b/linux/igb_uio/igb_uio.c
index ea439d131de1..33e0e0286b69 100644
--- a/linux/igb_uio/igb_uio.c
+++ b/linux/igb_uio/igb_uio.c
@@ -250,7 +250,7 @@ igbuio_pci_enable_interrupts(struct rte_uio_pci_dev *udev)
 		}
 #endif
 
-	/* falls through - to MSI */
+	fallthrough;
 	case RTE_INTR_MODE_MSI:
 #ifndef HAVE_ALLOC_IRQ_VECTORS
 		if (pci_enable_msi(udev->pdev) == 0) {
@@ -269,7 +269,7 @@ igbuio_pci_enable_interrupts(struct rte_uio_pci_dev *udev)
 			break;
 		}
 #endif
-	/* falls through - to INTX */
+	fallthrough;
 	case RTE_INTR_MODE_LEGACY:
 		if (pci_intx_mask_supported(udev->pdev)) {
 			dev_dbg(&udev->pdev->dev, "using INTX");
@@ -279,7 +279,7 @@ igbuio_pci_enable_interrupts(struct rte_uio_pci_dev *udev)
 			break;
 		}
 		dev_notice(&udev->pdev->dev, "PCI INTX mask not supported\n");
-	/* falls through - to no IRQ */
+	fallthrough;
 	case RTE_INTR_MODE_NONE:
 		udev->mode = RTE_INTR_MODE_NONE;
 		udev->info.irq = UIO_IRQ_NONE;
-- 
2.33.1