linux-kernel - Re: [PATCH v6 4/5] tty: serial: handle HAS

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Message-ID: <alpine.DEB.2.21.2410072109130.30973@angie.orcam.me.uk>
Date: Mon, 7 Oct 2024 22:09:15 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
cc: Brian Cain <bcain@...cinc.com>, Marcel Holtmann <marcel@...tmann.org>, 
    Luiz Augusto von Dentz <luiz.dentz@...il.com>, 
    Patrik Jakobsson <patrik.r.jakobsson@...il.com>, 
    Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
    Maxime Ripard <mripard@...nel.org>, 
    Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
    Simona Vetter <simona@...ll.ch>, Dave Airlie <airlied@...hat.com>, 
    Gerd Hoffmann <kraxel@...hat.com>, 
    Lucas De Marchi <lucas.demarchi@...el.com>, 
    Thomas Hellström <thomas.hellstrom@...ux.intel.com>, 
    Rodrigo Vivi <rodrigo.vivi@...el.com>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
    Heiko Carstens <hca@...ux.ibm.com>, linux-kernel@...r.kernel.org, 
    linux-hexagon@...r.kernel.org, linux-bluetooth@...r.kernel.org, 
    dri-devel@...ts.freedesktop.org, virtualization@...ts.linux.dev, 
    spice-devel@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org, 
    linux-serial@...r.kernel.org, linux-arch@...r.kernel.org, 
    Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH v6 4/5] tty: serial: handle HAS_IOPORT dependencies

On Mon, 7 Oct 2024, Niklas Schnelle wrote:

> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
> index 6709b6a5f3011db38acc58dc7223158fe4fcf72e..6a638feb44e443a1998980dd037748f227ec1bc8 100644
> --- a/drivers/tty/serial/8250/8250_pci.c
> +++ b/drivers/tty/serial/8250/8250_pci.c
[...]
>  	iobase = pci_resource_start(dev, 0);
>  	outb(0x0, iobase + CH384_XINT_ENABLE_REG);
>  }
>  
> -
>  static int
>  pci_sunix_setup(struct serial_private *priv,
>  		const struct pciserial_board *board,

 Gratuitous change here.

> diff --git a/drivers/tty/serial/8250/8250_pcilib.c b/drivers/tty/serial/8250/8250_pcilib.c
> index ea906d721b2c3eac15c9e8d62cc6fa56c3ef6150..fc1882d7515b5814ff1240ffdbe1009ab908ad6b 100644
> --- a/drivers/tty/serial/8250/8250_pcilib.c
> +++ b/drivers/tty/serial/8250/8250_pcilib.c
> @@ -28,6 +28,10 @@ int serial8250_pci_setup_port(struct pci_dev *dev, struct uart_8250_port *port,
>  		port->port.membase = pcim_iomap_table(dev)[bar] + offset;
>  		port->port.regshift = regshift;
>  	} else {
> +		if (!IS_ENABLED(CONFIG_HAS_IOPORT)) {
> +			pr_err("Serial port %lx requires I/O port support\n", port->port.iobase);
> +			return -EINVAL;
> +		}
>  		port->port.iotype = UPIO_PORT;
>  		port->port.iobase = pci_resource_start(dev, bar) + offset;
>  		port->port.mapbase = 0;

 Can we please flatten this conditional and get rid of the negation, and 
also use `pci_err' for clear identification (`port->port.iobase' may not 
even have been set to anything meaningful if this triggers)?  I.e.:

		/* ... */
	} else if (IS_ENABLED(CONFIG_HAS_IOPORT)) {
		/* ... */
	} else {
		pci_err(dev, "serial port requires I/O port support\n");
		return -EINVAL;
	}

I'd also say "port I/O" (by analogy to "memory-mapped I/O") rather than 
"I/O port", but I can imagine it might be debatable.

> +static __always_inline bool is_upf_fourport(struct uart_port *port)
> +{
> +	if (!IS_ENABLED(CONFIG_HAS_IOPORT))
> +		return false;
> +
> +	return port->flags & UPF_FOURPORT;
> +}

 Can we perhaps avoid adding this helper and then tweaking code throughout 
by having:

#ifdef CONFIG_SERIAL_8250_FOURPORT
#define UPF_FOURPORT		((__force upf_t) ASYNC_FOURPORT       /* 1  */ )
#else
#define UPF_FOURPORT		0
#endif

in include/linux/serial_core.h instead?  I can see the flag is reused by 
drivers/tty/serial/sunsu.c, but from a glance over it seems rubbish to me 
and such a change won't hurt the driver anyway.

> @@ -1174,7 +1201,7 @@ static void autoconfig(struct uart_8250_port *up)
>  		 */
>  		scratch = serial_in(up, UART_IER);
>  		serial_out(up, UART_IER, 0);
> -#ifdef __i386__
> +#if defined(__i386__) && defined(CONFIG_HAS_IOPORT)
>  		outb(0xff, 0x080);
>  #endif
>  		/*
> @@ -1183,7 +1210,7 @@ static void autoconfig(struct uart_8250_port *up)
>  		 */
>  		scratch2 = serial_in(up, UART_IER) & UART_IER_ALL_INTR;
>  		serial_out(up, UART_IER, UART_IER_ALL_INTR);
> -#ifdef __i386__
> +#if defined(__i386__) && defined(CONFIG_HAS_IOPORT)
>  		outb(0, 0x080);
>  #endif
>  		scratch3 = serial_in(up, UART_IER) & UART_IER_ALL_INTR;

 Nah, i386 does have machine OUTB instructions, it has the port I/O 
address space in the ISA, so these two changes make no sense to me.  

 Though this #ifdef should likely be converted to CONFIG_X86_32 via a 
separate change.

> @@ -1306,12 +1333,12 @@ static void autoconfig_irq(struct uart_8250_port *up)
>  {
>  	struct uart_port *port = &up->port;
>  	unsigned char save_mcr, save_ier;
> +	unsigned long irqs;
>  	unsigned char save_ICP = 0;
>  	unsigned int ICP = 0;
> -	unsigned long irqs;
>  	int irq;

 Gratuitous change here (also breaking the reverse Christmas tree order).

 Thanks for making the clean-ups we discussed.

  Maciej