[libata] fix oops on non-DMA bmdma hardware

Alan noted: "bmdma may be zero but the bmdma_irq_clear function gets
called even in this case during pure PIO operation. Check we have a
bmdma before we use it."

I fixed this by adding a check for zero.  While was I there, I fixed the
non-standard indentation of the small function's code.

Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 10 insertions, 7 deletions

diff --git a/drivers/scsi/libata-core.c b/drivers/scsi/libata-core.c
index 673ddf611d0e..c8d2201b126f 100644
--- a/drivers/scsi/libata-core.c
+++ b/drivers/scsi/libata-core.c
@@ -4202,14 +4202,17 @@ void ata_bmdma_setup(struct ata_queued_cmd *qc)
 
 void ata_bmdma_irq_clear(struct ata_port *ap)
 {
-    if (ap->flags & ATA_FLAG_MMIO) {
-        void __iomem *mmio = ((void __iomem *) ap->ioaddr.bmdma_addr) + ATA_DMA_STATUS;
-        writeb(readb(mmio), mmio);
-    } else {
-        unsigned long addr = ap->ioaddr.bmdma_addr + ATA_DMA_STATUS;
-        outb(inb(addr), addr);
-    }
+        if (!ap->ioaddr.bmdma_addr)
+                return;
 
+        if (ap->flags & ATA_FLAG_MMIO) {
+                void __iomem *mmio =
+                      ((void __iomem *) ap->ioaddr.bmdma_addr) + ATA_DMA_STATUS;
+                writeb(readb(mmio), mmio);
+        } else {
+                unsigned long addr = ap->ioaddr.bmdma_addr + ATA_DMA_STATUS;
+                outb(inb(addr), addr);
+        }
 }