[U-Boot] [PATCH v2] watchdog: Fix Watchdog Reset while in U-Boot Prompt

[Simon Glass]

+Tom, in case this should go into the release.

On 1 August 2016 at 05:49, Andreas J. Reichel
<Andreas.Reichel at tngtech.com> wrote:
> This patch fixes unwanted watchdog resets while the user enters
> a command at the U-Boot prompt.
>
> As found on the CM-FX6 board from Compulab, when having enabled the
> watchdog, a missing WATCHDOG_RESET call in _serial_tstc() in
> (/drivers/serial/serial-uclass.c) causes this and alike boards to
> reset when the watchdog's timeout has elapsed while waiting at the
> U-Boot prompt.
>
> Despite the user could press several keys within the watchdog
> timeout limit, the while loop in cli_readline.c, line 261, does only
> call WATCHDOG_RESET if first == 1, which gets set to 0 in the 1st
> loop iteration. This leads to a watchdog timeout no matter if the
> user presses keys or not.
>
> The problem is solved with a call to WATCHDOG_RESET in _serial_tstc,
> defined in drivers/serial/serial-uclass.c.
>
> Since the macro WATCHDOG_RESET expands to {} if watchdog support
> isn't configured, there's no need to surround it by #ifdef in this
> case.
>
>  * Symptom:
>    U-Boot resets after watchdog times out when in commandline prompt
>    and watchdog is enabled.
>
>  * Reasoning:
>    When U-Boot shows the commandline prompt, the following function
>    call stack is executed while waiting for a keypress:
>
>    common/main.c:
>                     main_loop          => common/cli.c: cli_loop() =>
>    common/cli_hush.c:
>                     parse_file_outer   => parse_stream_outer       =>
>                     parse_stream       => b_getch(i)               =>
>                     i->get(i)          => file_get                 =>
>                     get_user_input     => cmdedit_read_input       =>
>                     uboot_cli_readline =>
>    common/cli_readline.c:
>                     cli_readline       => cli_readline_into_buffer =>
>                     cread_line         => getcmd_getch (== getc)   =>
>    commonn/console.c:
>                     fgetc              => console_tstc
>
>    - in console_tstc line 181:
>    If dev->tstc(dev) returns 0, the global tstcdev variable doesn't
>    get set. This is the case if no character is in the serial buffer.
>
>    - in fgetc(int file), line 297:
>    Program flow keeps looping because tstcdev does not get set.
>    Therefore WATCHDOG_RESET is not called, as mx_serial_tstc from
>    drivers/serial/serial_mxc.c does not call it.
>
>    - Initialization calls drv_system_init in stdio.c, which sets
>    dev.tstc = stdio_serial_tstc. Thus, dev->tstc(dev) calls serial_tstc()
>    which in turn calls _serial_tstc().
>
>    Hence, _serial_tstc() needs to call WATCHDOG_RESET() to periodically
>    reset the watchdog while cli_readline waits for user input.
>
> Signed-off-by: Christian Storm <christian.storm at tngtech.com>
> Signed-off-by: Jan Kiszka <jan.kiszka at siemens.com>
> Signed-off-by: Andreas J. Reichel <Andreas.Reichel at tngtech.com>
> ---
>
> Changes in v2:
>  - Move WATCHDOG_RESET() call from common/console.c to
>    drivers/serial/serial-uclass.c.
>
>  drivers/serial/serial-uclass.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
> index 0ce5c44..72cf808 100644
> --- a/drivers/serial/serial-uclass.c
> +++ b/drivers/serial/serial-uclass.c
> @@ -155,6 +155,7 @@ static int _serial_tstc(struct udevice *dev)
>  {
>         struct dm_serial_ops *ops = serial_get_ops(dev);
>
> +       WATCHDOG_RESET();
>         if (ops->pending)
>                 return ops->pending(dev, true);

Great explanation, thank you.

Acked-by: Simon Glass <sjg at chromium.org>

>
> --
> 2.8.2
>