ARM: riscpc: fix DMA

DMA got broken a while back in two different ways:
1) a change in the behaviour of disable_irq() to wait for the interrupt
   to finish executing causes us to deadlock at the end of DMA.
2) a change to avoid modifying the scatterlist left the first transfer
   uninitialised.

DMA is only used with expansion cards, so has gone unnoticed.

Fixes: fa4e9989 ("[ARM] dma: RiscPC: don't modify DMA SG entries")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/mach-rpc/dma.c

@@ -131,7 +131,7 @@ static irqreturn_t iomd_dma_handle(int irq, void *dev_id)
 	} while (1);
 
 	idma->state = ~DMA_ST_AB;
-	disable_irq(irq);
+	disable_irq_nosync(irq);
 
 	return IRQ_HANDLED;
 }
@@ -174,6 +174,9 @@ static void iomd_enable_dma(unsigned int chan, dma_t *dma)
 				DMA_FROM_DEVICE : DMA_TO_DEVICE);
 		}
 
+		idma->dma_addr = idma->dma.sg->dma_address;
+		idma->dma_len = idma->dma.sg->length;
+
 		iomd_writeb(DMA_CR_C, dma_base + CR);
 		idma->state = DMA_ST_AB;
 	}