imx6q Uart receive data error "RX FIFO overrun"

[1282497337]

Hi,community

We use imx6q UART port to communicate and receive information from other device using RS485,The device will always send data, we have configured ttymxc3 to work at 576000 ,then I used imx6 UART to receive the data, when device always connect to the imx6 UART, it's can receive data well.

but when I cut it down afterwards link it again, I will got the error message from kernel 

imx-uart 21f0000.serial: Rx FIFO overrun

imx-uart 21f0000.serial: Rx FIFO overrun

imx-uart 21f0000.serial: Rx FIFO overrun

imx-uart 21f0000.serial: Rx FIFO overrun

...........................

Once I got the error I cannot receive data anymore,unless kill the application and open it again.

I used the Oscilloscope to measure the UART port (near the imx6 chip )waveform there is no problem , I got the signal and the signal is okey. we test all UART port and the error  it's same !

We have using 3.14.52 kernel,the board is imx6q-sabresd

Really appreciate any help!

Thanks very much

Alee

[igorpadykov]

Hi AL

one can try to reset uart using sect.64.10.2 Software reset i.MX6DQ Reference
Manual and if sdma was used, try to not use sdma.
https://www.nxp.com/docs/en/reference-manual/IMX6DQRM.pdf

Best regards
igor
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[1282497337]

Hi igor

As you know I used the sdma to transmit data,then for test i disable sdma and it can solve such problem (if i got FIFO overrun UART will continue receive data), unfortunately another peoblem arises that when I send data about 10000 Byte pre second use baud rate 115200 ,thread kworker occupy CPU about 15 present, I used baud rate 115200 * 10 and send data about 500000 Byte/sec kworker  occupy CPU over 85%. its cause many other problem ,

Could you give me some advise if i want to use sdma how to solve the problem that fifo overrun and cannot receive data anymore .

Looking forward to your suggestions!

thanks 

ALee

[1282497337]

Hi community

maybe I addressed this problem,but not sure.Blowe is my solution:

I'm using kernel 3.14.52 and I found the source code kernel/driver/tty/serial/imx.c will got the DMA transmit status but do not deal with it.

Imx.c (drivers\tty\serial)

static void dma_rx_callback(void *data)
{
          struct imx_port *sport = data;
          struct dma_chan *chan = sport->dma_chan_rx;
          struct tty_struct *tty = sport->port.state->port.tty;
          struct dma_tx_state state;
          enum dma_status status;
          unsigned int count;

          /* If we have finish the reading. we will not accept any more data. */
          if (tty->closing) {
                    imx_rx_dma_done(sport);
                    return;
          }

          status = dmaengine_tx_status(chan, (dma_cookie_t)0, &state); // to get DMA status but not care this return value "status"?

+        if(DMA_ERROR == status){

+               dmaengine_terminate_all(chan);

+               dmaengine_resume(chan);

+         }

          count = RX_BUF_SIZE - state.residue;
          sport->rx_buf.buf_info[sport->rx_buf.cur_idx].filled = true;
          sport->rx_buf.buf_info[sport->rx_buf.cur_idx].rx_bytes = count;
          sport->rx_buf.cur_idx++;
          sport->rx_buf.cur_idx %= IMX_RXBD_NUM;
          dev_dbg(sport->port.dev, "We get %d bytes.\n", count);

          if (sport->rx_buf.cur_idx == sport->rx_buf.last_completed_idx)
                    dev_err(sport->port.dev, "overwrite!\n");

          if (count)
                    dma_rx_work(sport);
}

The DMA status defined 

 Dmaengine.h (include\linux)

enum dma_status {
         DMA_COMPLETE,
         DMA_IN_PROGRESS,
         DMA_PAUSED,
         DMA_ERROR,
};

Under normal circumstances this "status == 1" this mean is DMA_IN_PROGRESS ,but sometimes I will got "status == 3", the DMA error occurred . then i can't receive  data from this serial port anymore  unless I closs  this uart and open it again.

now it's will continue receive data when i get "status == 3" DMA error .