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

Hi Hugo,

On Tue, 14 Jul 2026 at 16:40, Hugo Villeneuve <[email protected]> wrote:
> On Tue, 14 Jul 2026 11:59:54 +0200
> Geert Uytterhoeven <[email protected]> wrote:
> > 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";

That would be better, as "32be" is definitely wrong for UPIO_MEM32.

>
> > > +       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"?

Up to the serial maintainers.
I may be biassed, as I am usually working on systems where it prints zero ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds