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

From: Farouk Bouabid
Date: Thu Feb 08 2024 - 10:46:34 EST

Hi Christoph,

On 30.01.24 13:29, Christoph Niedermaier wrote:
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From: Farouk Bouabid
Sent: Monday, January 29, 2024 9:57 AM


On 26.01.24 20:58, Lino Sanfilippo wrote:
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On 26.01.24 18:27, Farouk Bouabid wrote:
From: Heiko Stuebner <heiko.stuebner@xxxxxxxxx>

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?

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

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