tree 8b041829bb43e44e0595800b4ae2bd866ba99161
parent bb63a1c7ae3fbf86e975a3672052a42d437ae5f4
author Pali Rohár <pali@kernel.org> 1636975496 +0100
committer Manish Pandey <manish.pandey2@arm.com> 1638463082 +0100

fix(plat/marvell/a3720/uart): do external reset during initialization

Sometimes when changing UART clock from TBG to XTAL, UART HW enters into
some broken state. It does not transit characters from TX FIFO anymore
and TX FIFO stays always empty. TX FIFO reset does not recover UART HW
from this broken state.

Experiments show that external reset can fix UART HW from this broken
state.

TF-A fatal error handler calls console_a3700_core_init() function to
initialize UART HW. This handler may be called anytime during CPU
runtime, also when kernel is running.

U-Boot or Linux kernel may change UART clock to TBG to achieve higher
baudrates. During initialization, console_a3700_core_init() resets UART
configuration to default settings, which means that it also changes
UART clock from TBG to XTAL.

Do an external reset of UART via North Bridge Peripheral reset register
to prevent this UART hangup.

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I8990bce24d1a6fd8ccc47a2cd0a5ff932fcfcf14