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Date: Thu, 8 Jul 2010 10:19:53 +0300
From: Gleb Natapov <gleb@redhat.com>
Message-ID: <20100708071953.GQ4689@redhat.com>
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Subject: [Qemu-devel] Re: [SeaBIOS] [PATCH] virtio: Clear interrupt status
 register in virtio-blk
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To: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: seabios@seabios.org, qemu-devel@nongnu.org

On Wed, Jul 07, 2010 at 01:34:22PM +0100, Stefan Hajnoczi wrote:
> 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@linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb@redhat.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

--
			Gleb.