linux-kernel - Re: [PATCH v4 3/6] dt-bindings: serial: add binding for rs485 rx-enable state when rs485 is disabled

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Date: Mon, 29 Jan 2024 17:22:07 +0000
From: Conor Dooley <conor@...nel.org>
To: Quentin Schulz <quentin.schulz@...obroma-systems.com>
Cc: 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>, 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
Subject: Re: [PATCH v4 3/6] dt-bindings: serial: add binding for rs485
 rx-enable state when rs485 is disabled

On Mon, Jan 29, 2024 at 01:26:51PM +0100, Quentin Schulz wrote:
> Hi Conor,
> 
> On 1/28/24 18:38, Conor Dooley wrote:
> > On Fri, Jan 26, 2024 at 03:55:12PM +0100, Farouk Bouabid wrote:
> > > RS485 can have a receiver-enable gpio (rx-enable-gpios). When rs485 is
> > > enabled, this gpio, if provided, must be driven active while receiving.
> > > However when RS485 is disabled this gpio should not have an undefined
> > > state. In that case, as DE and RE pins can be connected both to this gpio,
> > > if its state is not properly defined, can cause unexpected transceiver
> > > behavior.
> > > This binding depend on rx-enable-gpios to be implemented.
> > 
> > Why do you need a dedicated property for this when there exists a device
> > specific compatible for the uart on both of the affected rockchip
> > systems?
> > 
> 
> This has nothing to do with Rockchip's IP but the HW design of our
> carrierboard, so using the "rockchip,px30-uart" for that (which I assume is
> what was suggested here?) is incorrect since it'll also apply to PX30,
> RK3399 and RK3588-based Q7 SoCs we manufacture.
> 
> Did I understand the suggestion correctly?

Yes you did. That explanation for not being able to use the compatibles
makes sense. However, I can't give you an ack, because reading the
commit message gives me the same feeling as looking at this photo:
https://www.reddit.com/r/pics/comments/f8jyuz/nothing_in_this_image_is_identifiable/

Sorry,
Conor.

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