Re: [PATCH 1/1] tty: serial: handle HAS_IOPORT dependencies

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Fri, 2024-11-22 at 07:18 -0800, Guenter Roeck wrote:
> On Fri, Apr 05, 2024 at 05:29:24PM +0200, Niklas Schnelle wrote:
> > In a future patch HAS_IOPORT=n will disable inb()/outb() and friends at
> > compile time. We thus need to add HAS_IOPORT as dependency for those
> > drivers using them unconditionally. For 8250 based drivers some support
> > MMIO only use so fence only the parts requiring I/O ports.
> > 
> > Co-developed-by: Arnd Bergmann <arnd@kernel.org>
> > Signed-off-by: Arnd Bergmann <arnd@kernel.org>
> > Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ...
> > @@ -422,10 +443,12 @@ static void set_io_from_upio(struct uart_port *p)
> >  	up->dl_write = default_serial_dl_write;
> >  
> > +	default:
> > +		WARN(1, "Unsupported UART type %x\n", p->iotype);
> 
> So, according to this patch, the serial uart on microblaze, nios2,
> openrisc, xtensa, and possibly others is not or no longer supported.
> 
> WARNING: CPU: 0 PID: 0 at drivers/tty/serial/8250/8250_port.c:470 serial8250_set_defaults+0x1a8/0x22c
> Unsupported UART type 0
> 
> Any special reason ?
> 
> Guenter

So according to the warning the p->iotype is 0 which is UPIO_PORT.
For UPIO_PORT the switch above the WARN would pick io_serial_in() and
io_serial_out() as handlers. These use inb() respectively outb() to
access the serial so I don't see how they would work with !HAS_IOPORT
and it most definitely won't work for s390.

Now for Microblaze Kconfig says to select HAS_IOPORT if PCI so I'd
assume that it can use inb()/outb() and maybe the PCI requirement is
not correct if this isn't a PCI device and it used to work with
inb()/outb()? For nios2, openrisc, and xtensa they don't select
HAS_IOPORT so either it really won't work anyway or they should select
it. Can you tell us more about the devices involved where you saw this?

Thanks,
Niklas