topic mctrl_gpio_set empty? in i.MX Processors

mctrl_gpio_set empty?

jose_au_zone — Thu, 11 Feb 2021 05:07:12 GMT

Hello!

I'm trying to make RS-485 connection work in half-duplex mode on the i.MX8

Found this very similar problem here: https://community.nxp.com/t5/i-MX-Processors/Does-UART-in-RS485-mode-support-only-9-Bit-mode-for-i-MX6/m-p/699703

Looks like the solution was to add the rs485-enabled-at-boot-time property in the required uart node in the device tree. I searched in the kernel code and this is checked at the function uart_get_rs485_mode. If the property is present the SER_RS485_ENABLED flag is set

But digging deeper into the code, the function that should actually set the RTS pin to the required value is empty.
That function is mctrl_gpio_set which is called by both the function imx_uart_rts_active and imx_uart_rts_inactive

That can be checked here

I didn't test in my board yet to see if just adding the rs485-enabled-at-boot-time property enables the half-duplex comm. But I'm curious about why is that function empty in the kernel code

Thank you so much!

Re: mctrl_gpio_set empty?

igorpadykov — Thu, 11 Feb 2021 07:29:58 GMT

Hi jose_au_zone

seems it is used in imx.c using "SER_RS485_ENABLED",

https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/tty/serial/imx.c?h=imx_5.4.70_2.3.0

if (device_property_read_bool(dev, "linux,rs485-enabled-at-boot-time"))

rs485conf->flags |= SER_RS485_ENABLED;

https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/tty/serial/serial_core.c?h=imx_5.4.70_2.3.0

Best regards
igor

Re: mctrl_gpio_set empty?

jose_au_zone — Thu, 11 Feb 2021 15:54:43 GMT

Thanks for the reply. That I know already, but why the function that would change the RTS line to the appropriate level is empty? That's what I wanted to know

Thanks!

Re: mctrl_gpio_set empty?

igorpadykov — Fri, 12 Feb 2021 03:56:24 GMT

>why the function that would change the RTS line to the appropriate level is empty?

imx_uart_start_tx() seems changes the RTS line, it is not empty :

https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/tty/serial/imx.c?h=imx_5.4.70_2.3.0

Best regards
igor