linux-kernel - Re: [PATCH v2 6/7] serial: qcom-geni: drop flip buffer WARN()

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Message-ID: <CAD=FV=W9fEQ-g_LWK18SfZq4ZmFN_QbrBCwKRx3BTc0i-UXEcA@mail.gmail.com>
Date: Thu, 3 Oct 2024 13:06:43 -0700
From: Doug Anderson <dianders@...omium.org>
To: Johan Hovold <johan+linaro@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 6/7] serial: qcom-geni: drop flip buffer WARN()

Hi,

On Tue, Oct 1, 2024 at 5:51 AM Johan Hovold <johan+linaro@...nel.org> wrote:
>
> Drop the unnecessary WARN() in case the TTY buffers are ever full in
> favour of a rate limited dev_err() which doesn't kill the machine when
> panic_on_warn is set.
>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>  drivers/tty/serial/qcom_geni_serial.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 5b6c5388efee..8bc4b240bf59 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -570,9 +570,8 @@ static void handle_rx_uart(struct uart_port *uport, u32 bytes, bool drop)
>
>         ret = tty_insert_flip_string(tport, port->rx_buf, bytes);
>         if (ret != bytes) {
> -               dev_err(uport->dev, "%s:Unable to push data ret %d_bytes %d\n",
> -                               __func__, ret, bytes);
> -               WARN_ON_ONCE(1);
> +               dev_err_ratelimited(uport->dev, "failed to push data (%d < %u)\n",
> +                               ret, bytes);

Not that it really matters, but since you're fixing the type of
"bytes" to %u you probably should fix "ret" to %u too, which means
changing the type of it? Officially tty_insert_flip_string returns the
(unsigned) size_t.

As a nit, I'd also say that your error message shouldn't assert "<"
unless you change your "if" test to "<". It seems safer to use != so
IMO the printout should also say "!=".

I'd hope you're not hitting this error a lot because it means you're
dropping bytes, but getting rid of the WARN_ON and changing to
ratelimited makes sense to me.

Reviewed-by: Douglas Anderson <dianders@...omium.org>