linux-kernel - Re: [PATCH 1/1] tty: serial: handle HAS

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Message-ID: <3b75b92805648577ed05ff221d0c56e381aa1c7c.camel@linux.ibm.com>
Date: Fri, 22 Nov 2024 16:35:57 +0100
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby	
 <jirislaby@...nel.org>,
        Ilpo Järvinen	
 <ilpo.jarvinen@...ux.intel.com>,
        linux-serial@...r.kernel.org, Arnd
 Bergmann	 <arnd@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] tty: serial: handle HAS_IOPORT dependencies

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@...nel.org>
> > Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> > Signed-off-by: Niklas Schnelle <schnelle@...ux.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