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

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Date: Mon, 29 Jan 2024 09:57:11 +0100
From: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
To: Lino Sanfilippo <LinoSanfilippo@....de>,
 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 20:58, Lino Sanfilippo wrote:
> [Some people who received this message don't often get email from linosanfilippo@....de. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> 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.
What we are trying to implement is a gpio that emulates the RTS signal 
itself as we do not have a dedicated RTS signal that can be controlled 
through MCR. The rx during tx state in our case is a fixed state of 
"NO_RX_WHILE_TX"

Regards,

>