bcm2835-dma: Add support for per-channel flags

Add the ability to interpret the high bits of the dreq specifier as
flags to be included in the DMA_CS register. The motivation for this
change is the ability to set the DISDEBUG flag for SD card transfers
to avoid corruption when using the VPU debugger.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

drivers/dma/bcm2835-dma.c

@@ -141,6 +141,10 @@ struct bcm2835_desc {
 #define BCM2835_DMA_S_DREQ	BIT(10) /* enable SREQ for source */
 #define BCM2835_DMA_S_IGNORE	BIT(11) /* ignore source reads - read 0 */
 #define BCM2835_DMA_BURST_LENGTH(x) ((x & 15) << 12)
+#define BCM2835_DMA_CS_FLAGS(x) (x & (BCM2835_DMA_PRIORITY(15) | \
+				      BCM2835_DMA_PANIC_PRIORITY(15) | \
+				      BCM2835_DMA_WAIT_FOR_WRITES | \
+				      BCM2835_DMA_DIS_DEBUG))
 #define BCM2835_DMA_PER_MAP(x)	((x & 31) << 16) /* REQ source */
 #define BCM2835_DMA_WAIT(x)	((x & 31) << 21) /* add DMA-wait cycles */
 #define BCM2835_DMA_NO_WIDE_BURSTS BIT(26) /* no 2 beat write bursts */
@@ -454,7 +458,8 @@ static void bcm2835_dma_start_desc(struct bcm2835_chan *c)
 	c->desc = d = to_bcm2835_dma_desc(&vd->tx);
 
 	writel(d->cb_list[0].paddr, c->chan_base + BCM2835_DMA_ADDR);
-	writel(BCM2835_DMA_ACTIVE, c->chan_base + BCM2835_DMA_CS);
+	writel(BCM2835_DMA_ACTIVE | BCM2835_DMA_CS_FLAGS(c->dreq),
+	       c->chan_base + BCM2835_DMA_CS);
 }
 
 static irqreturn_t bcm2835_dma_callback(int irq, void *data)
@@ -481,7 +486,8 @@ static irqreturn_t bcm2835_dma_callback(int irq, void *data)
 	 * if this IRQ handler is threaded.) If the channel is finished, it
 	 * will remain idle despite the ACTIVE flag being set.
 	 */
-	writel(BCM2835_DMA_INT | BCM2835_DMA_ACTIVE,
+	writel(BCM2835_DMA_INT | BCM2835_DMA_ACTIVE |
+	       BCM2835_DMA_CS_FLAGS(c->dreq),
 	       c->chan_base + BCM2835_DMA_CS);
 
 	d = c->desc;