serial: 8250: Set Altera 16550 TX FIFO Threshold

The Altera 16550 soft IP UART requires 2 additional registers for
TX FIFO threshold support. These 2 registers enable the TX FIFO
Low Watermark and set the TX FIFO Low Watermark.
Set the TX FIFO threshold to the FIFO size - tx_loadsz.

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/uapi/linux/serial_reg.h b/include/uapi/linux/serial_reg.h
index 1e5ac4e776da..b4c04842a8c0 100644
--- a/include/uapi/linux/serial_reg.h
+++ b/include/uapi/linux/serial_reg.h
@@ -376,5 +376,13 @@
 #define UART_EXAR_TXTRG         0x0a    /* Tx FIFO trigger level write-only */
 #define UART_EXAR_RXTRG         0x0b    /* Rx FIFO trigger level write-only */
 
+/*
+ * These are definitions for the Altera ALTR_16550_F32/F64/F128
+ * Normalized from 0x100 to 0x40 because of shift by 2 (32 bit regs).
+ */
+#define UART_ALTR_AFR           0x40    /* Additional Features Register */
+#define UART_ALTR_EN_TXFIFO_LW  0x01    /* Enable the TX FIFO Low Watermark */
+#define UART_ALTR_TX_LOW        0x41    /* Tx FIFO Low Watermark */
+
 #endif /* _LINUX_SERIAL_REG_H */