Re: [PATCH v3 04/10] serial: uniformize serial port I/O infos display

Hi Geert,

On Tue, 14 Jul 2026 11:59:54 +0200
Geert Uytterhoeven <[email protected]> wrote:

> Hi Hugo,
> 
> On Thu, 21 May 2026 at 20:23, Hugo Villeneuve <[email protected]> wrote:
> > From: Hugo Villeneuve <[email protected]>
> >
> > Uniformize serial port I/O infos display from three different functions
> > that display mostly the same information, but with some variations, by
> > adding a common function.
> >
> > This make use of new functions uart_iotype_mmio() and
> > uart_iotype_legacy_io() to simplify and improve code readability.
> > This will prevent displaying irrelevant information for future IO types
> > (ex: UPIO_BUS), while also addressing the (eventually) invalid check for
> > "iotype >= UPIO_MEM".
> >
> > This also allows us to remove the confusing cast to (unsigned long long)
> > for iobase which is defined as an unsigned long, and use %pa to display the
> > mapbase pointer, as it is done in earlycon_print_info().
> >
> > Replace snprintf with more robust scnprintf so we could perhaps one day get
> > rid of snprintf() entirely.
> >
> > Signed-off-by: Hugo Villeneuve <[email protected]>
> 
> Thanks for your patch, which is now commit 86305190f307c05b ("serial:
> uniformize serial port I/O infos display") in tty/tty-next.
> 
> > Maybe the width information could be dropped entirely?
> 
> Perhaps...

I didn't receive any feedback about that during review...

> 
> > --- a/drivers/tty/serial/earlycon.c
> > +++ b/drivers/tty/serial/earlycon.c
> > @@ -75,19 +75,12 @@ static void __init earlycon_print_info(struct earlycon_device *device)
> >  {
> >         struct console *earlycon = device->con;
> >         struct uart_port *port = &device->port;
> > +       char ioinfos[64];
> >
> > -       if (port->iotype == UPIO_MEM || port->iotype == UPIO_MEM16 ||
> > -           port->iotype == UPIO_MEM32 || port->iotype == UPIO_MEM32BE)
> > -               pr_info("%s%d at MMIO%s %pa (options '%s')\n",
> > -                       earlycon->name, earlycon->index,
> > -                       (port->iotype == UPIO_MEM) ? "" :
> > -                       (port->iotype == UPIO_MEM16) ? "16" :
> > -                       (port->iotype == UPIO_MEM32) ? "32" : "32be",
> 
> This handled 32 vs 32be...

See answer below...

> 
> > -                       &port->mapbase, device->options);
> > -       else
> > -               pr_info("%s%d at I/O port 0x%lx (options '%s')\n",
> > -                       earlycon->name, earlycon->index,
> > -                       port->iobase, device->options);
> > +       uart_get_ioinfos(port, ioinfos, sizeof(ioinfos));
> > +
> > +       pr_info("%s%d%s (options '%s')\n", earlycon->name, earlycon->index,
> > +               ioinfos, device->options);
> >  }
> >
> >  static int __init parse_options(struct earlycon_device *device, char *options)
> 
> > @@ -2476,38 +2473,47 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
> >  }
> >  EXPORT_SYMBOL(uart_resume_port);
> >
> > +static const char *uart_get_mmio_width(struct uart_port *port)
> > +{
> > +       switch (port->iotype) {
> > +       case UPIO_MEM16:
> > +               return "16";
> > +       case UPIO_MEM32:
> 
> Missing
> 
>     return "32";
> 
> > +       case UPIO_MEM32BE:
> > +               return "32be";

I fact, this could probably be simplified as:

    case UPIO_MEM32:
    case UPIO_MEM32BE:
        return "32";

> > +       case UPIO_AU:
> > +       case UPIO_MEM:
> > +       default:
> > +               return "";
> > +       }
> > +}
> 
> >  static inline void
> >  uart_report_port(struct uart_driver *drv, struct uart_port *port)
> >  {
> > -       char address[64];
> > +       char ioinfos[64];
> >
> > -       switch (port->iotype) {
> > -       case UPIO_PORT:
> > -               snprintf(address, sizeof(address), "I/O 0x%lx", port->iobase);
> > -               break;
> > -       case UPIO_HUB6:
> > -               snprintf(address, sizeof(address),
> > -                        "I/O 0x%lx offset 0x%x", port->iobase, port->hub6);
> > -               break;
> > -       case UPIO_MEM:
> > -       case UPIO_MEM16:
> > -       case UPIO_MEM32:
> > -       case UPIO_MEM32BE:
> > -       case UPIO_AU:
> > -       case UPIO_TSI:
> > -               snprintf(address, sizeof(address),
> > -                        "MMIO 0x%llx", (unsigned long long)port->mapbase);
> > -               break;
> > -       default:
> > -               strscpy(address, "*unknown*", sizeof(address));
> > -               break;
> > -       }
> > +       uart_get_ioinfos(port, ioinfos, sizeof(ioinfos));
> >
> > -       pr_info("%s%s%s at %s (irq = %u, base_baud = %u) is a %s\n",
> > -              port->dev ? dev_name(port->dev) : "",
> > -              port->dev ? ": " : "",
> > -              port->name,
> > -              address, port->irq, port->uartclk / 16, uart_type(port));
> > +       pr_info("%s%s%s%s (irq = %u, base_baud = %u) is a %s\n",
> > +               port->dev ? dev_name(port->dev) : "",
> > +               port->dev ? ": " : "",
> > +               port->name, ioinfos, port->irq, port->uartclk / 16, uart_type(port));
> >
> >         /* The magic multiplier feature is a bit obscure, so report it too.  */
> >         if (port->flags & UPF_MAGIC_MULTIPLIER)
> 
> I am also wondering if the ", base_baud = %u" should be dropped if
> port->uartclk is zero.  But that is a pre-existing issue.

Ok, but I'm wondering which is better, to drop it entirely, or to have
a "base_baud = 0" displayed if port->uartclk is zero? I think I would
prefer the latter, or maybe "base_baud = N/A"?

Thank you for your comments.

-- 
Hugo Villeneuve