[PATCH v5 1/8] serial: 8250_dw: select port setup through platform data

[Ilpo Järvinen]

On Thu, 29 Oct 2026, James Hilliard wrote:

> Select feature discovery and DMA attachment through a platform-data setup
> callback. The generic callback probes the optional registers and attaches
> DMA when a FIFO size is available. Integrations with a fixed configuration
> can supply their own setup before the port is registered. Allow setup to
> return an error so integrations can reject invalid configuration before
> registration.
> 
> Replace skip_autocfg with the Octeon setup selection. Octeon is a 64-bit
> platform and continues to skip optional-register probing while retaining
> its DMA setup. Select the DMA setup helper directly for this integration.
> Keep generic setup for devices without matched platform data as well.
> 
> Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
> ---
>  drivers/tty/serial/8250/8250_dw.c | 41 ++++++++++++++++++++++++++++-----------
>  1 file changed, 30 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 9cbe076463e0..a546cf2de7b6 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -64,6 +64,7 @@ struct dw8250_platform_data {
>  	u8 usr_reg;
>  	u32 cpr_value;
>  	unsigned int quirks;
> +	int (*setup)(struct uart_port *p);
>  };
>  
>  struct dw8250_data {
> @@ -76,7 +77,6 @@ struct dw8250_data {
>  	struct clk		*pclk;
>  	struct reset_control	*rst;
>  
> -	unsigned int		skip_autocfg:1;
>  	unsigned int		uart_16550_compatible:1;
>  	unsigned int		in_idle:1;
>  
> @@ -596,7 +596,6 @@ static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data)
>  		p->serial_out = dw8250_serial_outq;
>  		p->flags = UPF_SKIP_TEST | UPF_SHARE_IRQ | UPF_FIXED_TYPE;
>  		p->type = PORT_OCTEON;
> -		data->skip_autocfg = true;
>  	}
>  #endif
>  
> @@ -631,6 +630,28 @@ static void dw8250_shutdown(struct uart_port *port)
>  	d->no_int_count = 0;
>  }
>  
> +static int dw8250_setup_dma(struct uart_port *p)
> +{
> +	struct dw8250_data *data = to_dw8250_data(p->private_data);
> +	struct uart_8250_port *up = up_to_u8250p(p);
> +
> +	/* DMA setup requires a FIFO */
> +	if (!p->fifosize)
> +		return 0;
> +
> +	data->data.dma.rxconf.src_maxburst = p->fifosize / 4;
> +	data->data.dma.txconf.dst_maxburst = p->fifosize / 4;
> +	up->dma = &data->data.dma;
> +
> +	return 0;
> +}
> +
> +static int dw8250_setup(struct uart_port *p)
> +{
> +	dw8250_setup_port(p);
> +	return dw8250_setup_dma(p);
> +}
> +
>  static int dw8250_probe(struct platform_device *pdev)
>  {
>  	struct uart_8250_port uart = {}, *up = &uart;
> @@ -765,19 +786,16 @@ static int dw8250_probe(struct platform_device *pdev)
>  
>  	dw8250_setup_dma_filter(p, data);
>  
> -	if (!data->skip_autocfg)
> -		dw8250_setup_port(p);
> +	if (data->pdata && data->pdata->setup)
> +		err = data->pdata->setup(p);
> +	else
> +		err = dw8250_setup(p);
> +	if (err)
> +		return err;
>  
>  	/* Use the BUSY-safe sequence for both integer and fractional divisors. */
>  	p->set_divisor = dw8250_set_divisor;
>  
> -	/* If we have a valid fifosize, try hooking up DMA */
> -	if (p->fifosize) {
> -		data->data.dma.rxconf.src_maxburst = p->fifosize / 4;
> -		data->data.dma.txconf.dst_maxburst = p->fifosize / 4;
> -		up->dma = &data->data.dma;
> -	}
> -
>  	data->data.uport = serial8250_register_8250_port(up);
>  	if (IS_ERR(data->data.uport))
>  		return PTR_ERR(data->data.uport);
> @@ -860,6 +878,7 @@ static const struct dw8250_platform_data dw8250_dw_apb = {
>  static const struct dw8250_platform_data dw8250_octeon_3860_data = {
>  	.usr_reg = OCTEON_UART_USR,
>  	.quirks = DW_UART_QUIRK_OCTEON,
> +	.setup = dw8250_setup_dma,
>  };
>  
>  static const struct dw8250_platform_data dw8250_armada_38x_data = {

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen at linux.intel.com>

-- 
 i.