[SeaBIOS] [PATCH] virtio: Clear interrupt status register in virtio-blk

[Stefan Hajnoczi]

The VRING_AVAIL_F_NO_INTERRUPT flag is a hint that interrupts should be
suppressed.  It does not guarantee that interrupts will not be raised.
Therefore, make sure to clear the interrupt after each virtio-blk read.
This avoids a stuck interrupt interfering with the OS loaded later in
the boot process.

Signed-off-by: Stefan Hajnoczi <stefanha at linux.vnet.ibm.com>
---
 src/virtio-blk.c |    6 ++++++
 src/virtio-pci.h |    4 ++++
 2 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/src/virtio-blk.c b/src/virtio-blk.c
index 16d9ad8..74af488 100644
--- a/src/virtio-blk.c
+++ b/src/virtio-blk.c
@@ -62,6 +62,12 @@ virtio_blk_read(struct disk_op_s *op)
 
     /* Reclaim virtqueue element */
     vring_get_buf(vq, NULL);
+
+    /* Clear interrupt status register.  Avoid leaving interrupts stuck if
+     * VRING_AVAIL_F_NO_INTERRUPT was ignored and interrupts were raised.
+     */
+    vp_get_isr(GET_GLOBAL(vdrive_g->ioaddr));
+
     return status == VIRTIO_BLK_S_OK ? DISK_RET_SUCCESS : DISK_RET_EBADTRACK;
 }
 
diff --git a/src/virtio-pci.h b/src/virtio-pci.h
index 9da761d..d21d5a5 100644
--- a/src/virtio-pci.h
+++ b/src/virtio-pci.h
@@ -71,6 +71,10 @@ static inline void vp_set_status(unsigned int ioaddr, u8 status)
    outb(status, ioaddr + VIRTIO_PCI_STATUS);
 }
 
+static inline u8 vp_get_isr(unsigned int ioaddr)
+{
+   return inb(ioaddr + VIRTIO_PCI_ISR);
+}
 
 static inline void vp_reset(unsigned int ioaddr)
 {
-- 
1.7.1