linux-kernel - Re: [PATCH v5 2/6] serial: 8250: Support separate rs485 rx-enable GPIO

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Date: Fri, 26 Jan 2024 20:58:47 +0100
From: Lino Sanfilippo <LinoSanfilippo@....de>
To: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>
Cc: Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 quentin.schulz@...obroma-systems.com,
 Heiko Stuebner <heiko.stuebner@...rry.de>
Subject: Re: [PATCH v5 2/6] serial: 8250: Support separate rs485 rx-enable
 GPIO


Hi,

On 26.01.24 18:27, Farouk Bouabid wrote:
> From: Heiko Stuebner <heiko.stuebner@...rry.de>
>
> 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-specific gpio that can be
> set depending on the RX_DURING_TX setting in the common em485 callbacks.
>

we just added the rx_during_tx_gpio to the serial core.
Why cant you use this GPIO for your purpose?

Regards,
Lino