[PATCH v4 2/5] serial: 8250: share the RX trigger conversion helper

[Ilpo Järvinen]

On Tue, 27 Oct 2026, James Hilliard wrote:

> Extract the receive-trigger threshold search into serial8250_bytes_to_fcr()
> so drivers with per-port threshold tables can use the same conversion as
> the generic 8250 implementation.
> 
> Include the unsupported-table check in the helper and preserve the existing
> nearest-lower selection and highest-encoding fallback.
> 
> Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
> ---
>  drivers/tty/serial/8250/8250.h      | 16 ++++++++++++++++
>  drivers/tty/serial/8250/8250_port.c | 12 +-----------
>  2 files changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index 21ed9c41b751..195ed58a2231 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -8,6 +8,7 @@
>   */
>  
>  #include <linux/bits.h>
> +#include <linux/errno.h>
>  #include <linux/serial_8250.h>
>  #include <linux/serial_core.h>
>  #include <linux/dmaengine.h>
> @@ -73,6 +74,21 @@ struct serial8250_config {
>  	unsigned int	flags;
>  };
>  
> +static inline int serial8250_bytes_to_fcr(const unsigned char *rxtrig_bytes,

This looks way to complicated to be inline function so I think it should 
be kept in 8250_port and exported from there.

> +					  unsigned char bytes)
> +{
> +	if (!rxtrig_bytes[UART_FCR_R_TRIG_BITS(UART_FCR_R_TRIG_00)])
> +		return -EOPNOTSUPP;
> +
> +	for (unsigned int i = 1; i < UART_FCR_R_TRIG_MAX_STATE; i++) {
> +		if (bytes < rxtrig_bytes[i])
> +			/* Use the nearest lower value */
> +			return (i - 1) << UART_FCR_R_TRIG_SHIFT;
> +	}
> +
> +	return UART_FCR_R_TRIG_11;
> +}
> +
>  enum uart_port_type {
>  	/* Internal 8250 only */
>  	UART_PORT_AIROHA		= 124,
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 36b2b0a2c05c..c332963dc2ed 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -3018,18 +3018,8 @@ static int fcr_get_rxtrig_bytes(struct uart_8250_port *up)
>  static int bytes_to_fcr_rxtrig(struct uart_8250_port *up, unsigned char bytes)
>  {
>  	const struct serial8250_config *conf_type = &uart_config[up->port.type];
> -	int i;
>  
> -	if (!conf_type->rxtrig_bytes[UART_FCR_R_TRIG_BITS(UART_FCR_R_TRIG_00)])
> -		return -EOPNOTSUPP;
> -
> -	for (i = 1; i < UART_FCR_R_TRIG_MAX_STATE; i++) {
> -		if (bytes < conf_type->rxtrig_bytes[i])
> -			/* Use the nearest lower value */
> -			return (--i) << UART_FCR_R_TRIG_SHIFT;
> -	}
> -
> -	return UART_FCR_R_TRIG_11;
> +	return serial8250_bytes_to_fcr(conf_type->rxtrig_bytes, bytes);
>  }
>  
>  static int do_get_rxtrig(struct tty_port *port)
> 
> 

-- 
 i.