Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
IronPort-SDR: rkZn9l1//fdEx+uNXJoiJ0ZFrdEk6SkG9Q/CyFSV0SvvvBIepSMWzHrxuYJcyePM8jasVza/23
 knMwkfiol0GA==
IronPort-SDR: edpFT0HIsEHMg/tLPRba1KhN2kNU/6sO0pnJBSTuDdi1YcvX5l4mugCCOZrI3uXuNCbo0U31Kp
 kNFvCspetNdg==
Date:   Mon, 30 Mar 2020 17:56:45 +0300
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Heiko Stuebner <heiko@sntech.de>
Cc:     gregkh@linuxfoundation.org, jslaby@suse.com,
        matwey.kornilov@gmail.com, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org, lukas@wunner.de,
        christoph.muellner@theobroma-systems.com,
        giulio.benetti@micronovasrl.com,
        Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Subject: Re: [PATCH v2 6/7] serial: 8250: Support separate rs485 rx-enable
 GPIO
Message-ID: <20200330145645.GX1922688@smile.fi.intel.com>
References: <20200325231422.1502366-1-heiko@sntech.de>
 <20200325231422.1502366-7-heiko@sntech.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200325231422.1502366-7-heiko@sntech.de>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Mar 26, 2020 at 12:14:21AM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
> 
> The RE signal is used to control the duplex mode of transmissions,
> aka receiving data while sending in full duplex mode, while stopping
> receiving data in half-duplex mode.
> 
> On a number of boards the !RE signal is tied to ground so reception
> is always enabled except if the UART allows disabling the receiver.
> This can be taken advantage of to implement half-duplex mode - like
> done on 8250_bcm2835aux.
> 
> Another solution is to tie !RE to RTS always forcing half-duplex mode.
> 
> And finally there is the option to control the RE signal separately,
> like done here by introducing a new rs485-specifc gpio that can be
> set depending on the RX_DURING_TX setting in the common em485 callbacks.


> +		if (port->rs485_re_gpio)

Redundant. Same for all other cases.

> +			gpiod_set_value(port->rs485_re_gpio, 1);


> +	port->rs485_re_gpio = devm_gpiod_get(dev, "rs485-rx-enable",
> +					       GPIOD_FLAGS_BIT_DIR_OUT);
> +	if (IS_ERR(port->rs485_re_gpio)) {
> +		ret = PTR_ERR(port->rs485_re_gpio);
> +		port->rs485_re_gpio = NULL;
> +		if (ret != -ENOENT) {
> +			if (ret != -EPROBE_DEFER)
> +				dev_err(dev, "Cannot get rs485-rx-enable-gpios\n");
> +			return ret;
> +		}
> +	}

NIH of gpiod_get_optional().

-- 
With Best Regards,
Andy Shevchenko