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Subject: Re: [Gta04-owner] [PATCH 0/4] UART slave device support - version 4
To: "H. Nikolaus Schaller" <hns@goldelico.com>,
        Mark Rutland <mark.rutland@arm.com>
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From: Andrey Vostrikov <andrey.vostrikov@cogentembedded.com>
Organization: Cogent Embedded
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Date: Fri, 15 Jan 2016 18:43:29 +0300
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Hi Nikolaus,

H. Nikolaus Schaller wrote:
> And IMHO nobody has described that he/she needs a solution to model the*data*  relationship
> for devices connected behind a tty port.

I am not sure if my case fits *data* relationship or not in this case. Some time ago I asked about state of your patches.
In my case I have supervising microcontroller unit (MCU) that is connected to one of UARTs on SoC.

This MCU implements several functions that will be implemented as MFD driver:
  - watchdog and system reset
  - NVMEM EEPROM
  - HWMON sensors
  - Input/power button
  - and similar low level functions

So in my case DTS binding looks like:

&uart3 {
	mcu {
		line-speed = <baud rate>;
		watchdog {
			timeout = <ms>;
			...other params...
		};
		eeprom {
			#address-cells
			#size-cells
			cell1 : cell@1 {
				reg = <1 2>;
			};
			cell2 : cell@2 {
				reg = <2 1>;
			};
		};
		hwmon {
			sensors-list = "voltage", "current", etc...;
		}
	}
}

This MCU receives commands and notifies MFD driver about events via UART protocol.
It looks like not really a slave though, more like a partnership from data flow point of view.

There is no user space code involved in this case as whole interactions are between drivers (just a kick to open /dev/ttyXXX using sys_open, as there is no way to start probe on uart_slave bus and assign line discipline).


Best regards,
Andrey