[ARM] Fix DMA handler race condition.

This fixes a race condition in the RiscPC DMA code, which causes
DMA for a channel to halt due to a race condition between the
hardware state machine and the software programming the next DMA
buffer.

arch/arm/mach-rpc/dma.c

@@ -57,7 +57,7 @@ static void iomd_get_next_sg(struct scatterlist *sg, dma_t *dma)
 		if (end > PAGE_SIZE)
 			end = PAGE_SIZE;
 
-		if (offset + (int) TRANSFER_SIZE > end)
+		if (offset + TRANSFER_SIZE >= end)
 			flags |= DMA_END_L;
 
 		sg->length = end - TRANSFER_SIZE;
@@ -95,9 +95,7 @@ static irqreturn_t iomd_dma_handle(int irq, void *dev_id, struct pt_regs *regs)
 		if (!(status & DMA_ST_INT))
 			return IRQ_HANDLED;
 
-		if (status & DMA_ST_OFL && !dma->sg)
-			break;
-
+		if ((dma->state ^ status) & DMA_ST_AB)
 			iomd_get_next_sg(&dma->cur_sg, dma);
 
 		switch (status & (DMA_ST_OFL | DMA_ST_AB)) {
@@ -105,17 +103,23 @@ static irqreturn_t iomd_dma_handle(int irq, void *dev_id, struct pt_regs *regs)
 		case DMA_ST_AB:				/* .IB */
 			iomd_writel(dma->cur_sg.dma_address, base + CURA);
 			iomd_writel(dma->cur_sg.length, base + ENDA);
+			dma->state = DMA_ST_AB;
 			break;
 
 		case DMA_ST_OFL | DMA_ST_AB:		/* OIB */
 		case 0:					/* .IA */
 			iomd_writel(dma->cur_sg.dma_address, base + CURB);
 			iomd_writel(dma->cur_sg.length, base + ENDB);
+			dma->state = 0;
 			break;
 		}
+
+		if (status & DMA_ST_OFL &&
+		    dma->cur_sg.length == (DMA_END_S|DMA_END_L))
+			break;
 	} while (1);
 
-	iomd_writeb(0, dma->dma_base + CR);
+	dma->state = ~DMA_ST_AB;
 	disable_irq(irq);
 
 	return IRQ_HANDLED;
@@ -152,6 +156,7 @@ static void iomd_enable_dma(dmach_t channel, dma_t *dma)
 		}
 
 		iomd_writeb(DMA_CR_C, dma_base + CR);
+		dma->state = DMA_ST_AB;
 	}
 		
 	if (dma->dma_mode == DMA_MODE_READ)
@@ -165,13 +170,11 @@ static void iomd_disable_dma(dmach_t channel, dma_t *dma)
 {
 	unsigned long dma_base = dma->dma_base;
 	unsigned long flags;
-	unsigned int ctrl;
 
 	local_irq_save(flags);
-	ctrl = iomd_readb(dma_base + CR);
-	if (ctrl & DMA_CR_E)
+	if (dma->state != ~DMA_ST_AB)
 		disable_irq(dma->dma_irq);
-	iomd_writeb(ctrl & ~DMA_CR_E, dma_base + CR);
+	iomd_writeb(0, dma_base + CR);
 	local_irq_restore(flags);
 }
 

include/asm-arm/mach/dma.h

@@ -41,6 +41,7 @@ struct dma_struct {
 	unsigned int	dma_base;	/* Controller base address	*/
 	int		dma_irq;	/* Controller IRQ		*/
 	struct scatterlist cur_sg;	/* Current controller buffer	*/
+	unsigned int	state;
 
 	struct dma_ops	*d_ops;
 };