linux-kernel - Re: [PATCH v1 29/31] serial: 8250_mxpcie: Add sysfs to control terminator

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Message-ID: <aS-mgjAQXR3OgmUF@moxa-ThinkCentre-M90t>
Date: Wed, 3 Dec 2025 10:54:58 +0800
From: Crescent Hsieh <crescentcy.hsieh@...a.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: gregkh@...uxfoundation.org, jirislaby@...nel.org,
	ilpo.jarvinen@...ux.intel.com, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v1 29/31] serial: 8250_mxpcie: Add sysfs to control
 terminator

On Mon, Dec 01, 2025 at 04:40:51AM +0200, Andy Shevchenko wrote:
> On Sun, Nov 30, 2025 at 12:46 PM Crescent Hsieh
> <crescentcy.hsieh@...a.com> wrote:
> >
> > Some Moxa PCIe serial board variants support software-controlled
> > termination resistors on each port. Users currently have no standardized
> > interface to enable or disable terminator state from userspace.
> >
> > This patch introduces the following:
> >
> > - EXPORT a new sysfs attribute `/sys/class/tty/*/mxpcie8250_terminator`
> >   to allow users to read or set the terminator state (enabled/disabled).
> > - Implement both CPLD-based and GPIO-based paths depending on board model.
> > - Track runtime terminator state in `struct mxpcie8250_port`.
> > - Serialize CPLD modifications using a new `board_lock` spinlock.
> >
> > Example usage:
> >
> >     # Enable terminator on ttyS*
> >     echo 1 > /sys/class/tty/ttyS*/mxpcie8250_terminator
> >
> >     # Check current state
> >     cat /sys/class/tty/ttyS*/mxpcie8250_terminator
> >     enabled
> 
> This introduces an ABI without documentation update. It's no go.

Just to confirm my understanding — for any new user-visible ABI such
as a sysfs attribute, the corresponding documentation under
Documentation/ABI/ must be included in the same patch/series?

---
Sincerely,
Crescent Hsieh