linux-kernel - Re: [PATCH v1 30/31] serial: 8250_mxpcie: Add sysfs to control pull state via CPLD

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Message-ID: <CAHp75VceYXN5jXrHjRujH9mXfxhccxVONyzkAHWJCDXHGi8iKw@mail.gmail.com>
Date: Mon, 1 Dec 2025 04:42:28 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Crescent Hsieh <crescentcy.hsieh@...a.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 30/31] serial: 8250_mxpcie: Add sysfs to control pull
 state via CPLD

On Sun, Nov 30, 2025 at 12:46 PM Crescent Hsieh
<crescentcy.hsieh@...a.com> wrote:
>
> Some Moxa PCIe boards provide a CPLD-controlled pull/bias state.
> Expose a per-port sysfs attribute to read and set the pull state from
> userspace.
>
> This patch:
> - Defines MOXA_CPLD_PULL_STATE_FLAG and {ENABLE,DISABLE} values.
> - Implements mxpcie8250_cpld_{set,get}_pull_state() with board_lock
>   to serialize CPLD access.
> - Exports "mxpcie8250_pull_state" in the driver's attr group.
> - Restricts support to CPLD-based models (CP118E-A-I, CP138E-A,
>   CP134EL-A, CP116E-A-A, CP116E-A-B); return -ENODEV on others.
>
> Example:
>   # Enable pull state on ttyS*
>   echo 1 > /sys/class/tty/ttyS*/mxpcie8250_pull_state
>
>   # Query pull state
>   cat /sys/class/tty/ttyS*/mxpcie8250_pull_state
>   enabled

Okay, this all reminds me of the pin control subsystem. It has already
established an interface to do things, why do we need this custom one
here?

-- 
With Best Regards,
Andy Shevchenko