linux-kernel - Re: [PATCH v5 10/14] serial: liteuart: separate rx loop from poll timer

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Date:   Mon, 21 Nov 2022 11:44:29 -0500
From:   "Gabriel L. Somlo" <gsomlo@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        kgugala@...micro.com, mholenko@...micro.com, joel@....id.au,
        david.abdurachmanov@...il.com, florent@...oy-digital.fr,
        ilpo.jarvinen@...ux.intel.com
Subject: Re: [PATCH v5 10/14] serial: liteuart: separate rx loop from poll
 timer

On Mon, Nov 21, 2022 at 11:16:14AM +0100, Geert Uytterhoeven wrote:
> Hi Gabriel,
> 
> On Fri, Nov 18, 2022 at 3:57 PM Gabriel Somlo <gsomlo@...il.com> wrote:
> > Convert the rx loop into its own dedicated function, and (for now)
> > call it from the poll timer. This is in preparation for adding irq
> > support to the receive path.
> >
> > Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
> > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> 
> Thanks for your patch!
> 
> Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> 
> > --- a/drivers/tty/serial/liteuart.c
> > +++ b/drivers/tty/serial/liteuart.c
> > @@ -68,10 +68,8 @@ static struct uart_driver liteuart_driver = {
> >  #endif
> >  };
> >
> > -static void liteuart_timer(struct timer_list *t)
> > +static void liteuart_rx_chars(struct uart_port *port)
> 
> So first you spin this off into a separate function, so it can be
> called from both the interrupt and polling paths.
> Later, in "[PATCH v5 12/14] serial: liteuart: add IRQ support for the
> RX path", you remove the call from the polling path...
 
That's right -- the polling path now calls the IRQ handler,
which, in turn, calls `liteuart_rx_chars()` (and later `*_tx_chars()`
as well).

The polling timer becomes just an alternative way to invoke the irq
handler, giving it a chance to take care of any pending transfers in
either/both directions.

Thanks,
--Gabriel
 
> >  {
> > -       struct liteuart_port *uart = from_timer(uart, t, timer);
> > -       struct uart_port *port = &uart->port;
> >         unsigned char __iomem *membase = port->membase;
> >         unsigned int status, ch;
> >
> > @@ -88,6 +86,14 @@ static void liteuart_timer(struct timer_list *t)
> >         }
> >
> >         tty_flip_buffer_push(&port->state->port);
> > +}
> > +
> > +static void liteuart_timer(struct timer_list *t)
> > +{
> > +       struct liteuart_port *uart = from_timer(uart, t, timer);
> > +       struct uart_port *port = &uart->port;
> > +
> > +       liteuart_rx_chars(port);
> >
> >         mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> >  }
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> 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