linux-kernel - Re: [PATCH 23/33] serial: 8250: extract serial8250_set

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Message-ID: <451ac044-6e91-4895-a5b3-cb30396436e5@kernel.org>
Date: Thu, 12 Jun 2025 12:01:29 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-serial <linux-serial@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 23/33] serial: 8250: extract serial8250_set_efr()

On 11. 06. 25, 14:58, Ilpo Järvinen wrote:
> On Wed, 11 Jun 2025, Jiri Slaby (SUSE) wrote:
> 
>> serial8250_do_set_termios() consists of many registers and up flags
>> settings. Extract all these into separate functions. This time, setting
>> of EFR for UART_CAP_EFR ports.
>>
>> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
>> ---
>>   drivers/tty/serial/8250/8250_port.c | 43 +++++++++++++++++------------
>>   1 file changed, 25 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
>> index 2c045a4369fc..0f16398cc86f 100644
>> --- a/drivers/tty/serial/8250/8250_port.c
>> +++ b/drivers/tty/serial/8250/8250_port.c
>> @@ -2768,6 +2768,30 @@ static void serial8250_set_ier(struct uart_port *port, struct ktermios *termios)
>>   	serial_port_out(port, UART_IER, up->ier);
>>   }
>>   
>> +static void serial8250_set_efr(struct uart_port *port, struct ktermios *termios)
>> +{
>> +	struct uart_8250_port *up = up_to_u8250p(port);
>> +	u8 efr_reg = UART_EFR;
>> +	u8 efr = 0;
>> +
>> +	if (!(up->capabilities & UART_CAP_EFR))
>> +		return;
>> +
>> +	/*
>> +	 * TI16C752/Startech hardware flow control.  FIXME:
>> +	 * - TI16C752 requires control thresholds to be set.
>> +	 * - UART_MCR_RTS is ineffective if auto-RTS mode is enabled.
>> +	 */
>> +	if (termios->c_cflag & CRTSCTS)
>> +		efr |= UART_EFR_CTS;
>> +
>> +	if (port->flags & UPF_EXAR_EFR)
> 
> I wonder if it is possible to trigger this at all? Only 8250_exar.c sets
> this flag and does not contain UART_CAP_EFR at all (nor uses
> UPF_BOOT_AUTOCONF)??

Impossible as far as I can tell nowadays. Likely since:
commit 6be254c2113d18984bae002b3b3dfc133cf56ac5
Author: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Date:   Wed Jul 31 20:05:56 2019 +0300

     serial: 8250_exar: No need to autoconfigure Exar ports

Andy?

The question is whether we need the code or we can drop it 8-).

> 
>> +		efr_reg = UART_XR_EFR;
>> +
>> +	serial_port_out(port, UART_LCR, UART_LCR_CONF_MODE_B);
>> +	serial_port_out(port, efr_reg, efr);
>> +}
>> +
>>   void
>>   serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>>   		          const struct ktermios *old)


-- 
js
suse labs