Thanks for your suggestion. It's important for me. I read the source code for dma_map_single again. I found that both of them(as first argument is dma or uart) worked well. But in my code I found that the *sport->port.dev->dma_mask is not zero. By contrast the dma_mask for dma device is zero. You are right. There should be dma device. But I also have a doubt here. Why I find many other driver use the first argument here rather than the dma device pointer. They usually use the device like uart. -----Original Message----- From: Russell King - ARM Linux [mailto:linux@xxxxxxxxxxxxxxxx] Sent: Sunday, January 05, 2014 10:51 PM To: Yuan Yao-B46683 Cc: Arnd Bergmann; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx Subject: Re: [PATCH] the eDMA support for the LPUART send driver On Sun, Jan 05, 2014 at 03:44:49PM +0100, Arnd Bergmann wrote: > On Friday 27 December 2013, Yuan Yao wrote: > > + 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. > > > + 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". -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
