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Commit c685af1108d7 ("serial: mvebu-uart: fix tx lost characters") fixed tx
lost characters at low baud rates but started causing tx lost characters
when kernel is going to power off or reboot.
TX_EMP tells us when transmit queue is empty therefore all characters were
transmitted. TX_RDY tells us when CPU can send a new character.
Therefore we need to use different check prior transmitting new character
and different check after all characters were sent.
This patch splits polling code into two functions: wait_for_xmitr() which
waits for TX_RDY and wait_for_xmite() which waits for TX_EMP.
When rebooting A3720 platform without this patch on UART is print only:
[ 42.699�
And with this patch on UART is full output:
[ 39.530216] reboot: Restarting system
Fixes: c685af1108d7 ("serial: mvebu-uart: fix tx lost characters")
Signed-off-by: Pali Rohár <pali@kernel.org>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201223191931.18343-1-pali@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
54ca955b5a