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

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Date: Thu, 8 Feb 2024 16:46:18 +0100
From: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
To: Christoph Niedermaier <cniedermaier@...electronics.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

Hi Christoph,


On 30.01.24 13:29, Christoph Niedermaier wrote:
> [Einige Personen, die diese Nachricht erhalten haben, erhalten häufig keine E-Mails von cniedermaier@...electronics.com. Weitere Informationen, warum dies wichtig ist, finden Sie unter https://aka.ms/LearnAboutSenderIdentification ]
>
> 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?


Yes that indeed serves our purpose. Thank you for the suggestion.


Regards

Farouk

>
>
> Regards
> Christoph