Ongoing Support for OMAP Serial Driver in Future Kernel Versions

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1

Hi,

What’s the best way to find out how long a legacy driver like the omap-serial driver will be supported in the kernel going forward?

We’ve swapped out the 8250 driver for the OMAP serial driver via the .config file, since the omap serial driver implements a 485 mode which, thus far, appears to be functioning correctly for our application. On the next spin of our board, we plan to realize more 485 channels using the omap-serial driver and GPIO lines.

We’re currently “baselined” on kernel 4.4.110, but if we need to upgrade to a newer kernel version at some point, this could be an issue if the OMAP-serial driver is obsoleted in a later kernel.

As of yet, we haven’t tested the RS485 mode which has been implemented in the 8250 serial driver in kernel 4.6 and later, but if there are known plans for dropping support for the omap-serial driver, then we will definitely test the 8250/RS485 implementation.

Thus far have looked at the following, and didn’t SEE any plans for obsolescence:

https://github.com/torvalds/linux/commits/master/drivers/tty/serial/omap-serial.c

Also, comments like the following lead me to believe that the omap-serial driver will be around as long as the omap platform
is still supported. It SOUNDS almost like the 8250 driver is generic for other platforms (e.g. other than OMAP) which
don’t support DMA.

  • Note: This driver is made separate from 8250 driver as we cannot

  • over load 8250 driver with omap platform specific configuration for

  • features like DMA, it makes easier to implement features like DMA and

  • hardware flow control and software flow control configuration with

  • this driver as required for the omap-platform

Any insight here would be greatly appreciated…

Thanks!

Jeff

2

Hi,

What's the best way to find out how long a legacy driver like the omap-serial driver will be supported in the kernel going forward?

It's not going anywhere till they are feature matching..

We've swapped out the 8250 driver for the OMAP serial driver via the .config file, since the omap serial driver implements a 485 mode which, thus far, appears to be functioning correctly for our application. On the next spin of our board, we plan to realize more 485 channels using the omap-serial driver and GPIO lines.

We're currently "baselined" on kernel 4.4.110, but if we need to upgrade to a newer kernel version at some point, this could be an issue if the OMAP-serial driver is obsoleted in a later kernel.

As of yet, we haven't tested the RS485 mode which has been implemented in the 8250 serial driver in kernel 4.6 and later, but if there are known plans for dropping support for the omap-serial driver, then we will definitely test the 8250/RS485 implementation.

Thus far have looked at the following, and didn't SEE any plans for obsolescence:

History for drivers/tty/serial/omap-serial.c - torvalds/linux · GitHub

Also, comments like the following lead me to believe that the omap-serial driver will be around as long as the omap platform
is still supported. It SOUNDS almost like the 8250 driver is generic for other platforms (e.g. other than OMAP) which
don't support DMA.

* Note: This driver is made separate from 8250 driver as we cannot
* over load 8250 driver with omap platform specific configuration for
* features like DMA, it makes easier to implement features like DMA and
* hardware flow control and software flow control configuration with
* this driver as required for the omap-platform

Yeah, that "was" pretty much the state of the 8250 driver circa 2.6.32

485 mode is really the only thing the omap driver does better at this
point in today's kernel..

Regards,

3

Thanks Robert!!

Would really like to test the 485 mode in the 8250 driver, but before that, we’re going to try to get 485 mode enabled on the FTDI FT4232 USB<->serial hub. We’ve ordered some FT4232 Mini Module evaluation boards for FT4232 (FT4232H chip + EEPROM + breakout pins + mini USB port).

The biggest what if at the moment is how to write to the onboard EEPROM from Linux. The FT4232 data sheet indicates that an external EEPROM needs to be attached to the FT4232H, and the RI/TXDEN flag in the EEPROM needs to be re-configured from the default state to enable 485 mode for each of the 4 serial channels. Thus far, https://www.acmesystems.it/CM3-HOME_ft4232_setup looks promising, as the EEPROM tools appear to be talking to our EEPROM-less FT4232H chip on our custom board. .

Plan to post up on our findings/stumbling blocks here. If we can get this working, then this MAY be of interest to those looking for a quick RS 485 solution.

Regards,

Jeff

4

And following is a link to the thread showing where we’re at regarding connecting the BB-X15 to the FT4232 Mini Module, development board:

http://beagleboard.org/discuss?place=msg%2Fbeagleboard%2FLjrZqmp8dGA%2FciOgBxRBCgAJ