Re: [PATCH] tty: serial: Work around warning backtrace in serial8250_set_defaults

[Stafford Horne]

On Thu, Dec 05, 2024 at 06:30:33AM -0800, Guenter Roeck wrote:
> Commit 7c7e6c8924e7 ("tty: serial: handle HAS_IOPORT dependencies")
> triggers warning backtraces on a number of platforms which don't support
> IO ports.
> 
> WARNING: CPU: 0 PID: 0 at drivers/tty/serial/8250/8250_port.c:470 serial8250_set_defaults+0x148/0x1d8
> Unsupported UART type 0
> 
> The problem is seen because serial8250_set_defaults() is called for
> all members of the serial8250_ports[] array even if that array is
> not initialized.
> 
> Work around the problem by only displaying the warning if the port
> type is not 0 (UPIO_PORT) or if iobase is set for the port.
> 
> Fixes: 7c7e6c8924e7 ("tty: serial: handle HAS_IOPORT dependencies")
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
> A complete fix will require a sequence of patches, which will have to be
> tested thoroughly and is thus not 6.13 material. This patch doesn't fix
> the underlying problem, but it is good enough for 6.13, or at least not
> worse than 6.12, while at the same time avoiding the warning backtrace.

This works on OpenRISC where I was seeing the issue.  Has someone comitted to
work on the root cause?

Tested-by: Stafford Horne <shorne@xxxxxxxxx>

>  drivers/tty/serial/8250/8250_port.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 4d63d80e78a9..649e74e9b52f 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -467,7 +467,8 @@ static void set_io_from_upio(struct uart_port *p)
>  		break;
>  #endif
>  	default:
> -		WARN(1, "Unsupported UART type %x\n", p->iotype);
> +		WARN(p->iotype != UPIO_PORT || p->iobase,
> +		     "Unsupported UART type %x\n", p->iotype);
>  		p->serial_in = no_serial_in;
>  		p->serial_out = no_serial_out;
>  	}
> -- 
> 2.45.2
> 
>