[PATCH 19.11 v2] 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>
---
Cc: Christian Ehrhardt <christian.ehrhardt@canonical.com>

v2:
* Add both dummy and attribute fallthrough macro definition to
  compatibility header.
---
 kernel/linux/igb_uio/compat.h  | 14 ++++++++++++++
 kernel/linux/igb_uio/igb_uio.c |  6 +++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/kernel/linux/igb_uio/compat.h b/kernel/linux/igb_uio/compat.h
index 8dbb896ae118..850b359f3643 100644
--- a/kernel/linux/igb_uio/compat.h
+++ b/kernel/linux/igb_uio/compat.h
@@ -152,3 +152,17 @@ static inline bool igbuio_kernel_is_locked_down(void)
 	return false;
 #endif
 }
+
+#ifndef fallthrough
+
+#ifndef __has_attribute
+#define __has_attribute(x) 0
+#endif
+
+#if __has_attribute(__fallthrough__)
+#define fallthrough	__attribute__((__fallthrough__))
+#else
+#define fallthrough	do {} while (0)
+#endif
+
+#endif
diff --git a/kernel/linux/igb_uio/igb_uio.c b/kernel/linux/igb_uio/igb_uio.c
index 039f5a5f6354..57d0c58ab1b8 100644
--- a/kernel/linux/igb_uio/igb_uio.c
+++ b/kernel/linux/igb_uio/igb_uio.c
@@ -236,7 +236,7 @@ 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) {
@@ -255,7 +255,7 @@ 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");
@@ -265,7 +265,7 @@ 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