linux-kernel - Re: [PATCH v1 11/31] serial: 8250_mxpcie: enable enhanced mode and custom FIFO trigger levels

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Message-ID: <CAHp75VfbpnMWqRUZTw+UzxrnnfWsHn2dgqVpz2WDQo5PW-sgEQ@mail.gmail.com>
Date: Sun, 30 Nov 2025 21:25:24 +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 11/31] serial: 8250_mxpcie: enable enhanced mode and
 custom FIFO trigger levels

On Sun, Nov 30, 2025 at 12:44 PM Crescent Hsieh
<crescentcy.hsieh@...a.com> wrote:
>
> Add support for enabling enhanced mode and configuring custom FIFO
> trigger levels on Moxa PCIe serial boards.
>
> Enhanced mode is activated via EFR[4] and SFR[5], which is required to
> access special function registers used for advanced features. Once
> enhanced mode is enabled, custom TX/RX FIFO trigger levels and flow
> control thresholds are configured through specific registers.

...

> +static int mxpcie8250_startup(struct uart_port *port)
> +{
> +       struct uart_8250_port *up = up_to_u8250p(port);
> +       int i, ret;

Should "i" be signed?

> +       ret = serial8250_do_startup(port);

Same Q here: Why do we continue if we know it failed already?

> +       for (i = 0; i < 5; ++i)
> +               serial_out(up, UART_FCR, UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT);
> +
> +       serial_out(up, MOXA_PUART_EFR, MOXA_PUART_EFR_ENHANCED);
> +       serial_out(up, MOXA_PUART_SFR, MOXA_PUART_SFR_950);
> +
> +       serial_out(up, MOXA_PUART_TTL, 0);
> +       serial_out(up, MOXA_PUART_RTL, 96);
> +       serial_out(up, MOXA_PUART_FCL, 16);
> +       serial_out(up, MOXA_PUART_FCH, 110);
> +
> +       return ret;
> +}

-- 
With Best Regards,
Andy Shevchenko