cciss: disable DMA refetch on Smart Array P600

This patch disables DMA refetch in the PCI bridge. We have disabled DMA
prefetch for quite some time. Testing with XEN revealed another ASIC bug. If
dom0 resides on a P600 the board can can an MCA bi accessing invalid memory
addresses. Apparently, we need to disable both prefetch and refetch.
My understanding is a refetch operation should not occur but it is a valid
thing to do if prefetched data is no longer available for whatever reason.
Please consider this patch for inclusion.
Signed-off-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: Alex Chiang <achiang@hp.com>

--------------------------------------------------------------------------------
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/cciss.c

@@ -3035,15 +3035,20 @@ static int cciss_pci_init(ctlr_info_t *c, struct pci_dev *pdev)
 	}
 #endif
 
-	/* Disabling DMA prefetch for the P600
-	 * An ASIC bug may result in a prefetch beyond
-	 * physical memory.
+	/* Disabling DMA prefetch and refetch for the P600.
+	 * An ASIC bug may result in accesses to invalid memory addresses.
+	 * We've disabled prefetch for some time now. Testing with XEN
+	 * kernels revealed a bug in the refetch if dom0 resides on a P600.
 	 */
 	if(board_id == 0x3225103C) {
 		__u32 dma_prefetch;
+		__u32 dma_refetch;
 		dma_prefetch = readl(c->vaddr + I2O_DMA1_CFG);
 		dma_prefetch |= 0x8000;
 		writel(dma_prefetch, c->vaddr + I2O_DMA1_CFG);
+		pci_read_config_dword(pdev, PCI_COMMAND_PARITY, &dma_refetch);
+		dma_refetch |= 0x1;
+		pci_write_config_dword(pdev, PCI_COMMAND_PARITY, dma_refetch);
 	}
 
 #ifdef CCISS_DEBUG