[PATCH v4 3/7] serial: rsci: Enable transmit end interrupt in rsci_stop_tx()

[Diogo Ivo <diogo.ivo.sx@renesas.com>]

Currently, rsci_stop_tx() clears CCR0.TIE without enabling CCR0.TEIE.
If transmission is stopped while CCR0.TE is set (for example, via
TCOOFF), the hardware FIFO drains and sets CSR.TDRE while CCR0.TIE is 0,
and no TEI (Transmit End) interrupt is generated to clear CCR0.TE.

However, on RSCI setting TIE while TE is already set does not generate a
TXI interrupt. Thus, if transmission is later resumed via rsci_start_tx(),
setting CCR0.TIE while CCR0.TE and CSR.TDRE are already 1 fails to call
into rsci_transmit_chars(), permanently stalling subsequent transmissions.

Fix this by setting CCR0.TEIE in rsci_stop_tx() whenever CCR0.TE is
set, ensuring sci_tx_end_interrupt() fires once the hardware finishes
shifting out in-flight data and clears CCR0.TE.

Fixes: 0666e3fe95ab ("serial: sh-sci: Add support for RZ/T2H SCI")
Cc: stable@vger.kernel.org
Signed-off-by: Diogo Ivo <diogo.ivo.sx@renesas.com>
---
 drivers/tty/serial/rsci.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/rsci.c b/drivers/tty/serial/rsci.c
index 0391111db8ae..05703bb31afd 100644
--- a/drivers/tty/serial/rsci.c
+++ b/drivers/tty/serial/rsci.c
@@ -409,6 +409,8 @@ static void rsci_stop_tx(struct uart_port *port)
 
 	ctrl = rsci_serial_in(port, CCR0);
 	ctrl &= ~CCR0_TIE;
+	if (ctrl & CCR0_TE)
+		ctrl |= CCR0_TEIE;
 	rsci_serial_out(port, CCR0, ctrl);
 }
 

-- 
2.56.0