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Date:   Fri, 18 May 2018 17:19:49 -0500
From:   Rob Herring <robh@kernel.org>
To:     Radu Pirea <radu.pirea@microchip.com>
Cc:     devicetree@vger.kernel.org, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-spi@vger.kernel.org, mark.rutland@arm.com,
        lee.jones@linaro.org, gregkh@linuxfoundation.org, jslaby@suse.com,
        richard.genoud@gmail.com, alexandre.belloni@bootlin.com,
        nicolas.ferre@microchip.com, broonie@kernel.org
Subject: Re: [PATCH v3 2/6] mfd: at91-usart: added mfd driver for usart
Message-ID: <20180518221949.GA13443@rob-hp-laptop>
References: <20180511103822.31698-1-radu.pirea@microchip.com>
 <20180511103822.31698-3-radu.pirea@microchip.com>
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On Fri, May 11, 2018 at 01:38:18PM +0300, Radu Pirea wrote:
> This mfd driver is just a wrapper over atmel_serial driver and
> spi-at91-usart driver. Selection of one of the drivers is based on a
> property from device tree. If the property is not specified, the default
> driver is atmel_serial.
> 
> Signed-off-by: Radu Pirea <radu.pirea@microchip.com>
> ---
>  drivers/mfd/Kconfig                  | 10 ++++
>  drivers/mfd/Makefile                 |  1 +
>  drivers/mfd/at91-usart.c             | 75 ++++++++++++++++++++++++++++
>  include/dt-bindings/mfd/at91-usart.h | 17 +++++++
>  4 files changed, 103 insertions(+)
>  create mode 100644 drivers/mfd/at91-usart.c
>  create mode 100644 include/dt-bindings/mfd/at91-usart.h
> 

> +#ifndef __DT_BINDINGS_AT91_USART_H__
> +#define __DT_BINDINGS_AT91_USART_H__
> +
> +#define AT91_USART_MODE_SERIAL	1
> +#define AT91_USART_MODE_SPI	2

Won't this require a DT update for serial mode to add the mode property? 
That breaks compatibility.

Rob