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 ..." Changes in v3: * add macro STDIO_DEV_ASSIGN_FLUSH() * fix commit messages * remove changes from serial.c Changes in v2: * split one big patch into smaller 6 patches * add config option to allow disabling this new function Pali Rohár (6): sandbox: Add function os_flush() console: Implement flush() function serial: Implement flush callback serial: Implement serial_flush() function for console flush() fallback serial: Call flush() before changing baudrate boot: Call flush() before booting arch/sandbox/cpu/os.c | 5 +++ boot/bootm_os.c | 1 + cmd/boot.c | 1 + cmd/elf.c | 2 ++ cmd/load.c | 5 +++ common/Kconfig | 6 ++++ common/console.c | 64 ++++++++++++++++++++++++++++++++++ common/stdio.c | 8 +++++ drivers/serial/serial-uclass.c | 31 ++++++++++++++++ include/_exports.h | 3 ++ include/os.h | 8 +++++ include/serial.h | 5 +++ include/stdio.h | 15 ++++++++ include/stdio_dev.h | 7 ++++ 14 files changed, 161 insertions(+) -- 2.20.1
