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

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Date: Tue, 30 Jan 2024 12:29:47 +0000
From: Christoph Niedermaier <cniedermaier@...electronics.com>
To: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>, 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-kernel@...r.kernel.org>, "linux-serial@...r.kernel.org"
	<linux-serial@...r.kernel.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-rockchip@...ts.infradead.org"
	<linux-rockchip@...ts.infradead.org>, "quentin.schulz@...obroma-systems.com"
	<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

From: Farouk Bouabid
Sent: Monday, January 29, 2024 9:57 AM

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"

Why can't the property rts-gpios be used here for this purpose?


Regards
Christoph