AM4372: Receive dummy data by uart driver while the DMA is enabled

user2013294

Part Number: AM4372

Hi,

In our design(processor is AM4372, linux kernel is 4.9.69), the processor communicates with device by uart interface, to improve the performance of uart interface we enable DMA in dts file as below:

After the DMA is enabled, we find the processor receive some dummy data sometimes. we expect the normal data is:

Correct Data: 4c|b|0|8|0|8|0|8|0|8|77|

But we receive below data:

4c|b|0|8|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|8|0|8|0|8|77|

which many zeros are inserted in this message.

I also disable the DMA to try same testing. and confirm that this issue disappears while we disable the DMA of uart driver.

Do you have any idea about this issue?

thanks,

Johnny

over 5 years ago

0 Bin Liu over 5 years ago

TI__Guru**** 181436 points

Hi Johnny,

Which UART port do you use?

0 user2013294 over 5 years ago in reply to Bin Liu

Prodigy 210 points

Hi Bin,

We use UART1.

thanks,

Johnny

0 Bin Liu over 5 years ago in reply to user2013294

TI__Guru**** 181436 points

Hi Johnny,

Linux kernel doesn't enable DMA by default for AM437x UART, but you could add DMA support for UART port 0/4/5, but not port 1/2/3. The two groups use different UART IP, and port 1/2/3 have a hw issue which prevent DMA to function properly.

0 user2013294 over 5 years ago in reply to Bin Liu

Prodigy 210 points

Hi Bin,

Thank you.

Do you have any document about this HW issue?

Best Regards,

Johnny

0 Bin Liu over 5 years ago in reply to user2013294

TI__Guru**** 181436 points

Hi Johnny,

We don't have a public document for this issue yet, but we are in the process of updating the Errata to include it.

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AM4372: Receive dummy data by uart driver while the DMA is enabled