On Sun, Jan 05, 2014 at 03:44:49PM +0100, Arnd Bergmann wrote:

On Friday 27 December 2013, Yuan Yao wrote:

quoted

+	dma_phys = dma_map_single(sport->port.dev,
+				sport->port.state->xmit.buf,
+				UART_XMIT_SIZE, DMA_TO_DEVICE);

This is wrong: Since the dma is performed by the dma engine rather
than the uart, the first argument here needs to be the dma device
pointer. In fact, dma_map_single is normally supposed to fail on
the uart device as the dma_mask value should be zero. Not sure
why this worked.

quoted

+	if (!dma_phys) {
+		dev_err(sport->port.dev, "Dma_phys single failed\n");
+		return -ENOMEM;
+	}

Please also change all references to "phys" -- it's not a phys
address but a bus address. These are often the same, but that's
not for the driver to know.

This is also not how you test for failure of dma_map_single().  I
recommend reading the documentation for the APIs you're trying to
use...  Hint: dma_mapping_error().

-- 
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".