Marek reports, that the -next commit 1788cf6a (tty: serial: switch
from circ_buf to kfifo) broke meson_uart and qcom_geni_serial. The
commit mistakenly advanced the kfifo twice: once by
uart_fifo_get()/kfifo_out() and second time by uart_xmit_advance().

To advance the fifo only once, drop the superfluous uart_xmit_advance()
from both.

To count the TX statistics properly, use uart_fifo_out() in
qcom_geni_serial (meson_uart_start_tx() already uses that).

I checked all other uses of uart_xmit_advance() and they appear correct:
either they are finishing DMA transfers or are after peek/linear_ptr
(i.e. they do not advance fifo).
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: 1788cf6a ("tty: serial: switch from circ_buf to kfifo")
Cc: Neil Armstrong <neil.armstrong@linaro.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20240416054825.6211-1-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>