serial: pl011: Don't enable RX DMA if residue processing not supported

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@arm.com>

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 9c738c83fb8a6b767bf6cc5e7daa691c4ce8e6fd..9a94b3d0ddf61aeea811a5b601a8aa3e2efd7ae3 100644 (file)
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -304,7 +304,7 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *
 
        /* Optionally make use of an RX channel as well */
        chan = dma_request_slave_channel(dev, "rx");
-       
+
        if (!chan && plat->dma_rx_param) {
                chan = dma_request_channel(mask, plat->dma_filter, plat->dma_rx_param);
 
@@ -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;