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AM4376: Issue with RS-485 interface in latest kernel

Frank Walzer
Mastermind 44306 points
Part Number: AM4376

My customer ran into an issue when testing RS-485 interfaces using SDK 8.02.00.24 (Kernel 5.10). This resulted in missing communication during system test. Same HW with earlier SDK 4.03.00.05 (Kernel 4.9) is working.

In addition they ported omap-serial.c from 4.9 to 5.10. This is also working. They are asking for 5.10 release with a working RS-485 driver. Any info what was recently changed in that drivers?

Regards, Frank

  • +1
    TI__Guru**** 168211 points

    Hi Frank,

    When the customer is having issue with RS-485, do they use the forward-ported omap-serial.c or 8250-omap.c?

    In the new kernels, omap-serial.c is deprecated, only 8250-oma.c is supported for UART.

  • 0 in reply to Bin Liu
    TI__Mastermind 44306 points

    Hi Bin,

    sorry, once more I hit the wrong button. This is not yet resolved... Now I was not aware there is a new driver for RS-485 interfaces. Can you please point us to some docs for that? omap-serial.c seems to work in both kernels. Customer provided a patch that I could share offline.

    Thanks, Frank

  • 0 in reply to Frank Walzer
    TI__Guru 69632 points

    Hi Frank! The subject owner is currently out of the office. Please allow a couple of days for a response. Thanks.

  • +1 in reply to Frank Walzer
    TI__Guru**** 168211 points

    Hi Frank,

    Sorry for my late response.

    I want to clarify, 8250-omap.c is not a new RS-485 driver, rather a new UART driver for all TI processors. omap-serial.c has not been maintained for quite some time.

    8250-omap.c is a UART driver integrated to kernel 8250 framework, while omap-serial.c is under kernel serial framework. There is no dedicated documentation for this driver, since it is transparent to user space applications which should use the standard Linux tty interface.

    But I want to point out that the device tree settings for both 8250-omap.c and omap-serial.c have some difference, because both drivers are under different kernel frameworks. The DT differences are documented in kernel Documentation Documentation/devicetree/bindings/serial/.