[PATCH] console: Implement flush() function

[Simon Glass]

Hi Pali,

On Wed, 23 Feb 2022 at 06:34, Pali Rohár <pali at kernel.org> wrote:
>
> On certain places it is required to flush output print buffers to ensure
> that text strings were sent to console or serial devices. For example when
> printing message that U-Boot is going to boot kernel or when U-Boot is
> going to change baudrate of terminal device.
>
> Some console devices, like UART, have putc/puts functions which just put
> characters into HW transmit queue and do not wait until all data are
> transmitted. Doing some sensitive operations (like changing baudrate or
> starting kernel which resets UART HW) cause that U-Boot messages are lost.
>
> Therefore introduce a new flush() function, implement it for all serial
> devices via pending(false) callback and use this new flush() function on
> sensitive places after which output device may go into reset state.
>
> This change fixes printing of U-Boot messages:
> "## Starting application at ..."
> "## Switch baudrate to ..."
>
> Signed-off-by: Pali Rohár <pali at kernel.org>
> ---
>  arch/sandbox/cpu/os.c          |  5 +++
>  boot/bootm_os.c                |  1 +
>  cmd/boot.c                     |  1 +
>  cmd/elf.c                      |  2 ++
>  cmd/load.c                     |  5 +++
>  common/console.c               | 56 ++++++++++++++++++++++++++++++++++
>  common/stdio.c                 |  6 ++++
>  drivers/serial/serial-uclass.c | 25 +++++++++++++++
>  drivers/serial/serial.c        |  1 +
>  include/_exports.h             |  1 +
>  include/os.h                   |  8 +++++
>  include/serial.h               |  2 ++
>  include/stdio.h                |  7 +++++
>  include/stdio_dev.h            |  2 ++
>  14 files changed, 122 insertions(+)

There is a lot going on in this patch and I think it should be split
into a small series, something like:

- driver model changes (don't forget to update test/dm/serial.c)
- stdio changes
- sandbox changes
- plumbing into certain commands

You must not implement new features in the non-DM code as we are
migrating away from that. So just implement it for driver model.

Also, given the code-size impact I think this should have a Kconfig option.

Regards,
Simon