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

[Guenter Roeck]

On Thu, Dec 05, 2024 at 07:12:42PM +0000, Stafford Horne wrote:
> 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?
> 
Yes, Arnd is working on it.

Guenter

> 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
> > 
> >