[dpdk-stable] [PATCH] igb_uio: fix build on Linux 5.3 for implicit fall through

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

build error:
.../dpdk/build/build/kernel/linux/igb_uio/igb_uio.c:
   In function ‘igbuio_pci_enable_interrupts’:
   .../dpdk/build/build/kernel/linux/igb_uio/igb_uio.c:230:6:
   error: this statement may fall through
   [-Werror=implicit-fallthrough=]
  230 |   if (pci_alloc_irq_vectors(udev->pdev, 1, 1, ....
.../dpdk/build/build/kernel/linux/igb_uio/igb_uio.c:240:2:
   note: here
  240 |  case RTE_INTR_MODE_MSI:
      |  ^~~~

The build error is caused by Linux kernel commit in 5.3 that enables the
"-Wimplicit-fallthrough=3" gcc flag.
Commit a035d552a93b ("Makefile: Globally enable fall-through warning")

To fix the error, either a gcc attribute can be provided [1] or a code
comment with some defined syntax need to be provided [2], since there is
already comments, updated them slightly to match the required syntax to
fix the build error.

[1]
"__attribute__ ((fallthrough));"

[2]
[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?
fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?

Cc: stable@dpdk.org

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
---
 kernel/linux/igb_uio/igb_uio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/linux/igb_uio/igb_uio.c b/kernel/linux/igb_uio/igb_uio.c
index 3cf394bdf..039f5a5f6 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
 
-	/* fall back to MSI */
+	/* falls through - to MSI */
 	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
-	/* fall back to INTX */
+	/* falls through - to INTX */
 	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");
-	/* fall back to no IRQ */
+	/* falls through - to no IRQ */
 	case RTE_INTR_MODE_NONE:
 		udev->mode = RTE_INTR_MODE_NONE;
 		udev->info.irq = UIO_IRQ_NONE;
-- 
2.21.0