[PATCH 4/5] serial: pl011: Don't enable RX DMA if residue processing not supported

[Andrew Jackson]

If the DMA engine doesn't support residue processing then the RX DMA
handling won't work terribly well if polling is enabled.  So, disable
RX DMA if residue handling isn't available.

Signed-off-by: Andrew Jackson <Andrew.Jackson at arm.com>
---
 drivers/tty/serial/amba-pl011.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 7c5e263..79b9c93 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -322,7 +322,22 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *
 			.src_maxburst = uap->fifosize >> 2,
 			.device_fc = false,
 		};
+		struct dma_slave_caps caps;
 
+		/*
+		 * Some DMA controllers provide information on their capabilities.
+		 * If the controller does, check for suitable residue processing
+		 * otherwise assime all is well.
+		 */
+		if (0 == dma_get_slave_caps(chan, &caps)) {
+			if (caps.residue_granularity ==
+					DMA_RESIDUE_GRANULARITY_DESCRIPTOR) {
+				dma_release_channel(chan);
+				dev_info(uap->port.dev,
+					"RX DMA disabled - no residue processing\n");
+				return;
+			}
+		}
 		dmaengine_slave_config(chan, &rx_conf);
 		uap->dmarx.chan = chan;
 
-- 
1.7.1