Hi Fabio, On Sun, Jan 08, 2017 at 07:46:29PM -0200, Fabio Estevam wrote: > > What's the revision of the i.MX6Q on your board? Mine is 1.5 (TO 1.3) > > Mine is a mx6solo rev1.1. Could it be dependent upon SMP? Do you have an i.MX6Q board around to try? -- I made a few interesting discoveries in the meantime: 1) If I do not enable UCR4_TCEN, the data on TXD is fine. Of course the TE pin does not toggle in that case, but it shows that the problem has something to do with the actions taking place after the transmit complete interrupt and not with the hardware or DMA internals. 2) I added a few custom printks when doing echo A > /dev/ttymxc4 in RS-485 mode: imx_start_tx imx_dma_tx: tx_bytes=2, xmit->tail=0, xmit->head=2 imx_dma_tx: dma_tx_nents=1 imx-uart 21f4000.serial: TX: prepare to send 2 bytes by DMA imx_transmit_buffer: xmit->tail set to 1, xmit->head=2 imx_transmit_buffer: xmit->tail set to 2, xmit->head=2 imx_stop_tx (returns immediately because dma_is_txing) ^ repeats multiple times imx_stop_tx (goes through) dma_tx_callback: xmit->tail=2 tx_bytes=2 dma_tx_callback: xmit->tail set to 4 imx-uart 21f4000.serial: we finish the TX DMA. dma_tx_callback: xmit->tail=4 icount.tx=4 imx_dma_tx: tx_bytes=4094, xmit->tail=4, xmit->head=2 (!!) imx_dma_tx: dma_tx_nents=2 .. That's why the data is garbled in that way: It wraps around the circular buffer. xmit->tail jumps over xmit->head, which explains why I first see the correct characters, then again followed by many zeros and at the end again the correct characters. Regards, Clemens -- 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
