linux-kernel - Re: Wrong RS485 RTS polarity in 8250 OMAP UART Driver vs DT binding?

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Date:   Thu, 16 Mar 2023 10:51:26 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Francesco Dolcini <francesco@...cini.it>
Cc:     Vignesh Raghavendra <vigneshr@...com>, Bin Liu <b-liu@...com>,
        linux-serial@...r.kernel.org, Zeng Chao <chao.zeng@...mens.com>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        ilpo.jarvinen@...ux.intel.com, tony@...mide.com,
        andriy.shevchenko@...ux.intel.com,
        matthias.schiffer@...tq-group.com, linux-kernel@...r.kernel.org,
        Max Krummenacher <max.krummenacher@...adex.com>
Subject: Re: Wrong RS485 RTS polarity in 8250 OMAP UART Driver vs DT binding?

On Wed, Mar 15, 2023 at 09:41:56PM +0100, Francesco Dolcini wrote:
> We have working hardware, using another UART that expect
> rs485-rts-active-low, and the exact same HW, when using OMAP uart,
> requires rs485-rts-active-high (the HW is modular, so we are really just
> changing the uart, keeping the same RS485 transceiver / connections).
> 
> What's going on there? Is the semantic of the 8250_omap driver just the
> opposite as it should be?

Yes, sadly, for historic reasons.

See these threads:

https://lore.kernel.org/linux-serial/20220329085050.311408-1-matthias.schiffer@ew.tq-group.com/

https://lore.kernel.org/linux-serial/2de36eba3fbe11278d5002e4e501afe0ceaca039.1663863805.git.lukas@wunner.de/


> Am I doing something wrong in the device tree?

No, but regrettably you need a separate device tree depending on which SoC
you're using.

Thanks,

Lukas