Re: [PATCH v6 4/5] tty: serial: handle HAS_IOPORT dependencies

[Niklas Schnelle]

On Mon, 2024-10-07 at 22:09 +0100, Maciej W. Rozycki wrote:
> 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.

Agree this looks better, will change it.

> 
> > +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.

I'll look at this, do you think this is okay regarding matching the
user-space definitions in include/uapi/linux/tty_flags.h?

> 
> > @@ -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.

This is needed for Usermode Linux (UM) which sets __i386__ but also
doesn't have CONFIG_HAS_IOPORT. This was spotted by the kernel test bot
here: https://lore.kernel.org/all/202410031712.BwfGjrQY-lkp@xxxxxxxxx/

> 
> > @@ -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

WIll drop this hunk