From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrey Vostrikov <av.linux.dev@gmail.com>
Subject: MFD device driver on top of UART/RS232
Date: Mon, 16 Nov 2015 19:24:58 +0300
Message-ID: <564A035A.3050108@gmail.com>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Return-path: <linux-embedded-owner@vger.kernel.org>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20120113;
        h=from:subject:to:message-id:date:user-agent:mime-version
         :content-type:content-transfer-encoding;
        bh=+6ddgSSpXlJ3GD9K9n3akylizH4wWJ9k8+4mPHAglkw=;
        b=MRql7bjlIJg7xCyufnRr9Hv75xAZVtYB06Q+zw9LmR8H0wAMK//5Q0TQf/bstmH+pg
         9lfdQv4qS9aUcOrJufhVeEHwTJ4p8qqx26GbjtuWMWWa1i+R6ppyR0vnaFBYks8dN2l0
         23WDmcr6m4xl5cCP2tg+Pki6RPOMqSydV+SQjAioxBMxMe54Rj1CDpFoEiLi3Mo9KhwX
         8vLSHMuPoKM35M/kWNpkWck1GKMVpLkaRjIYkpwB7qwhq3OFU8ZX10h95/yoGbRBfP1f
         RABXpVAWlVgk25F90v8o6GZRRWhJa3f/AvXohFwos8Et4pxcEJad8ONJjwS/4imaz6A6
         QSMg==
Sender: linux-embedded-owner@vger.kernel.org
List-ID: <linux-embedded.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"; format="flowed"
To: linux-serial@vger.kernel.org, linux-embedded@vger.kernel.org

Hi,

I have an embedded system with microcontroller connected via UART/RS232 port. This microcontroller implements several low-level functions that need to be exposed as device drivers in other subsystems (watchdog, LEDs, HWMON, firmware read/write).

I checked many drivers implemented in the kernel, searched through mail list archives and it looks like there are three different ways to solve this task:
A) most of the devices that are connected using UART have user space program that configures and manages it (either directly or with help of dedicated line discipline, SLIP, SL-CAN, etc)
B) serio - mostly used for input devices
C) direct use of UART port taking control from serial_core.

The best match I have found so far is MFD driver for Atmel Microcontroller on iPaq h3xxx (drivers/mfd/ipaq-micro.c) that follows concept "C)"

Is this a good enough example to use for this task? This platform is a legacy one so I am confused a little if new driver will fit nicely into the mainline.

It would be great if someone could point me to another example to follow or advise better way to implement MFD driver without user space involvement.

Best regards,
Andrey