linux-kernel - Re: [RFC v2 34/39] tty: serial: add HAS

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Message-ID: <alpine.DEB.2.21.2205020341140.64520@angie.orcam.me.uk>
Date:   Mon, 2 May 2022 10:15:00 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-pci@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [RFC v2 34/39] tty: serial: add HAS_IOPORT dependencies

On Fri, 29 Apr 2022, Niklas Schnelle wrote:

> In a future patch HAS_IOPORT=n will result in inb()/outb() and friends
> not being declared. We thus need to add HAS_IOPORT as dependency for
> those drivers using them.
[...]
> diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> index cd93ea6eed65..e216bf745e78 100644
> --- a/drivers/tty/serial/8250/Kconfig
> +++ b/drivers/tty/serial/8250/Kconfig
> @@ -6,7 +6,7 @@
>  
>  config SERIAL_8250
>  	tristate "8250/16550 and compatible serial support"
> -	depends on !S390
> +	depends on HAS_IOPORT
>  	select SERIAL_CORE
>  	select SERIAL_MCTRL_GPIO if GPIOLIB
>  	help

 Similarly here some 8250-compatible platform or PCI/e serial port devices 
use MMIO, e.g.:

serial8250.0: ttyS2 at MMIO 0x1f000900 (irq = 20, base_baud = 230400) is a 16550A

or:

0001:01:00.0: ttyS0 at MMIO 0x600c080401000 (irq = 40, base_baud = 15625000) is a 16C950/954

so this has to be sorted out within the driver rather than by disabling it 
altogether.  Possibly with a suitable conditional wired to HAS_IOPORT in 
`set_io_from_upio' in drivers/tty/serial/8250/8250_port.c.

  Maciej