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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 55dc00d..d984a97 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -322,7 +322,22 @@
.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;