From 2d3b7d6e7dc8785f9a6c0e4d38188dd1a0859d11 Mon Sep 17 00:00:00 2001 From: Andrew Jackson Date: Fri, 7 Nov 2014 14:14:47 +0000 Subject: [PATCH] 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 Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/amba-pl011.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 55dc00dd0e5e..d984a97043b3 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; -- 2.34.1