serial: 8250: don't lost port's default capabilities

Commit b0b8c84cf58d ("serial: of_serial: Handle auto-flow-control
property") added support for fifo-size and hw-flow-control properties
to avoid adding new types to 8250.c for UARTs that are compatible with
the standard types but that have different size fifo or support 16750
compatible auto flow control. We avoided many new 8250 port types with
this nice feature, but there's a problem, if the code detects fifo-size
or auto-flow-control property, up->capabilities will be set
accordingly, then serial8250_set_defaults() will ignore the default
port's capabilities:

|if (!up->capabilities)
|	up->capabilities = uart_config[type].flags;

If the port's default capabilities contains other bits such as
UART_CAP_SLEEP, UART_CAP_EFR and so on, they are lost.

Fixes: b0b8c84cf58d ("serial: of_serial: Handle auto-flow-control property")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 drivers/tty/serial/8250/8250_port.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

On Sat, Jul 06, 2024 at 04:29:28PM +0800, Jisheng Zhang wrote:
> Commit b0b8c84cf58d ("serial: of_serial: Handle auto-flow-control
> property") added support for fifo-size and hw-flow-control properties
> to avoid adding new types to 8250.c for UARTs that are compatible with
> the standard types but that have different size fifo or support 16750
> compatible auto flow control. We avoided many new 8250 port types with
> this nice feature, but there's a problem, if the code detects fifo-size
> or auto-flow-control property, up->capabilities will be set
> accordingly, then serial8250_set_defaults() will ignore the default
> port's capabilities:
> 
> |if (!up->capabilities)
> |	up->capabilities = uart_config[type].flags;
> 
> If the port's default capabilities contains other bits such as
> UART_CAP_SLEEP, UART_CAP_EFR and so on, they are lost.
> 
> Fixes: b0b8c84cf58d ("serial: of_serial: Handle auto-flow-control property")
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 

Hi,

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Hi

On 16:29 Sat 06 Jul     , Jisheng Zhang wrote:
> Commit b0b8c84cf58d ("serial: of_serial: Handle auto-flow-control
> property") added support for fifo-size and hw-flow-control properties
> to avoid adding new types to 8250.c for UARTs that are compatible with
> the standard types but that have different size fifo or support 16750
> compatible auto flow control. We avoided many new 8250 port types with
> this nice feature, but there's a problem, if the code detects fifo-size
> or auto-flow-control property, up->capabilities will be set
> accordingly, then serial8250_set_defaults() will ignore the default
> port's capabilities:

> 
> |if (!up->capabilities)
> |	up->capabilities = uart_config[type].flags;
> 
so the previous old logic is trying to override the config of 'type' uart,
while this patch try to extend capabilities with default config of 'type' uart as base

I tend to agree this is right direction (but wasn't 100% sure..)

btw, Jisheng, can you also check serial8250_do_startup()? which has similar logic

> If the port's default capabilities contains other bits such as
> UART_CAP_SLEEP, UART_CAP_EFR and so on, they are lost.
> 
> Fixes: b0b8c84cf58d ("serial: of_serial: Handle auto-flow-control property")

I believe the commit just reveal the problem, make it more visible, but not the root cause,
'git blame' lead to b6830f6df8914f ("serial: 8250: Split base port operations from universal driver")
as the original commit introduce this logic which seems exist long time ago..


> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 893bc493f662..e20614241229 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -3245,8 +3245,7 @@ void serial8250_set_defaults(struct uart_8250_port *up)
>  			up->port.fifosize = uart_config[type].fifo_size;
>  		if (!up->tx_loadsz)
>  			up->tx_loadsz = uart_config[type].tx_loadsz;
> -		if (!up->capabilities)
> -			up->capabilities = uart_config[type].flags;
> +		up->capabilities |= uart_config[type].flags;
>  	}
>  
>  	set_io_from_upio(port);
> -- 
> 2.43.0
>