linux-kernel - Re: [PATCH v1 20/31] serial: 8250: add optional callbacks for rx_trig

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Message-ID: <CAHp75Veqh2fbsMBeBEBJ_ook0jZz_y=WALrgjJ0skLR9SWC0pQ@mail.gmail.com>
Date: Mon, 1 Dec 2025 03:58:18 +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 20/31] serial: 8250: add optional callbacks for rx_trig_bytes

On Sun, Nov 30, 2025 at 12:45 PM Crescent Hsieh
<crescentcy.hsieh@...a.com> wrote:
>
> The rx_trig_bytes sysfs attribute adjusts the UART RX FIFO trigger
> level. Some modern 8250 variants require programming device-specific
> registers to change this threshold, which the generic (FCR-based) path
> does not cover.
>
> This patch adds two optional uart_port callbacks:
>   - set_rxtrig(port, bytes): program a device-specific RX trigger threshold
>   - get_rxtrig(port):        read back the current RX trigger threshold
>
> When these callbacks are provided, the 8250 core will use them to
> set/read the hardware-specific threshold. If the callbacks are not
> implemented, the code falls back to the legacy generic path, so existing
> drivers keep their current behavior.
>
> No functional change for drivers that do not implement the new
> callbacks.

...

> -       rxtrig_bytes = do_serial8250_get_rxtrig(port);
> +       if (uport->get_rxtrig)
> +               rxtrig_bytes = uport->get_rxtrig(uport);
> +       else
> +               rxtrig_bytes = do_serial8250_get_rxtrig(port);

> +

Unneeded blank line.

>         if (rxtrig_bytes < 0)
>                 return rxtrig_bytes;

...

> -       ret = do_serial8250_set_rxtrig(port, bytes);
> +       if (uport->set_rxtrig)
> +               ret = uport->set_rxtrig(uport, bytes);
> +       else
> +               ret = do_serial8250_set_rxtrig(port, bytes);

> +

Ditto.

>         if (ret < 0)
>                 return ret;

-- 
With Best Regards,
Andy Shevchenko