[PATCH 1/2] serial: 8250: Add RX trigger levels for U6_16550A

["Kryštof Černý via B4 Relay" <devnull+cleverline1mc.gmail.com@kernel.org>]

From: Kryštof Černý <cleverline1mc@gmail.com>

PORT_U6_16550A has a 64-byte FIFO but no rxtrig_bytes table, so the
rx_trig_bytes sysfs attribute is not registered for ports of this type
and the RX trigger level cannot be read or changed from userspace.

Add a table with 1, 16, 32 and 62 bytes, i.e. 1 character, FIFO 1/4
full, FIFO 1/2 full and FIFO 2 less than full. These are the levels the
Synopsys DesignWare UART uses for a 64-byte FIFO, and they match the
existing PORT_ALTR_16550_F64 table.

The default FCR value of the type is unchanged, so the trigger level a
port starts with stays at 1/2 full. The only visible change for ports
already detected as U6_16550A by autoconfig is the new sysfs attribute.

This prepares for 8250_dw selecting PORT_U6_16550A for DesignWare UARTs
with a 64-byte FIFO.

Co-developed-by: Miroslav Ondra <ondra@faster.cz>
Signed-off-by: Miroslav Ondra <ondra@faster.cz>
Signed-off-by: Kryštof Černý <cleverline1mc@gmail.com>
---
 drivers/tty/serial/8250/8250_port.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 36b2b0a2c05c..a7acede62f40 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -163,6 +163,7 @@ static const struct serial8250_config uart_config[] = {
 		.fifo_size	= 64,
 		.tx_loadsz	= 64,
 		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10,
+		.rxtrig_bytes	= {1, 16, 32, 62},
 		.flags		= UART_CAP_FIFO | UART_CAP_AFE,
 	},
 	[PORT_TEGRA] = {

-- 
2.47.3