linux-kernel - Re: [PATCH V3 1/3] serial: stm32: remove infinite loop possibility in putchar function

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Message-ID: <CAMuHMdVCeuC5qStugnssWKUeOVWxd_3XyYtS0mrZpqQVaXAP2w@mail.gmail.com>
Date:   Tue, 19 Apr 2022 10:59:38 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Valentin Caron <valentin.caron@...s.st.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 1/3] serial: stm32: remove infinite loop possibility in
 putchar function

Hi Valentin,

On Tue, Apr 19, 2022 at 10:54 AM Valentin Caron
<valentin.caron@...s.st.com> wrote:
> Rework stm32_usart_console_putchar() function in order to anticipate
> the case where the character can never be sent.
>
> Signed-off-by: Valentin Caron <valentin.caron@...s.st.com>

Thanks for your patch!

> --- a/drivers/tty/serial/stm32-usart.c
> +++ b/drivers/tty/serial/stm32-usart.c
> @@ -1640,10 +1640,16 @@ static void stm32_usart_console_putchar(struct uart_port *port, unsigned char ch
>  {
>         struct stm32_port *stm32_port = to_stm32_port(port);
>         const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
> +       u32 isr;
> +       int ret;
>
> -       while (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
> -               cpu_relax();
> -
> +       ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr, isr,
> +                                               (isr & USART_SR_TXE), 100,
> +                                               STM32_USART_TIMEOUT_USEC);
> +       if (ret != 0) {
> +               dev_err(port->dev, "Error while sending data in UART TX : %d\n", ret);

Does it make sense to print this message, i.e. will the user ever see it?
Or is the failure above temporary?
I assume that you have seen this trigger?

> +               return;
> +       }
>         writel_relaxed(ch, port->membase + ofs->tdr);
>  }

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