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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>
This commit is contained in:
Thor Thayer 2016-09-22 14:56:16 -05:00 committed by Greg Kroah-Hartman
parent ffea043965
commit 8e5470c983
2 changed files with 51 additions and 0 deletions
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43
drivers/tty/serial/8250/8250_port.c
View File

@ -1870,6 +1870,30 @@ static int exar_handle_irq(struct uart_port *port)
return ret;
}
/*
* Newer 16550 compatible parts such as the SC16C650 & Altera 16550 Soft IP
* have a programmable TX threshold that triggers the THRE interrupt in
* the IIR register. In this case, the THRE interrupt indicates the FIFO
* has space available. Load it up with tx_loadsz bytes.
*/
static int serial8250_tx_threshold_handle_irq(struct uart_port *port)
{
unsigned long flags;
unsigned int iir = serial_port_in(port, UART_IIR);
/* TX Threshold IRQ triggered so load up FIFO */
if ((iir & UART_IIR_ID) == UART_IIR_THRI) {
struct uart_8250_port *up = up_to_u8250p(port);
spin_lock_irqsave(&port->lock, flags);
serial8250_tx_chars(up);
spin_unlock_irqrestore(&port->lock, flags);
}
iir = serial_port_in(port, UART_IIR);
return serial8250_handle_irq(port, iir);
}
static unsigned int serial8250_tx_empty(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
@ -2159,6 +2183,25 @@ int serial8250_do_startup(struct uart_port *port)
serial_port_out(port, UART_LCR, 0);
}
/*
* For the Altera 16550 variants, set TX threshold trigger level.
*/
if (((port->type == PORT_ALTR_16550_F32) ||
(port->type == PORT_ALTR_16550_F64) ||
(port->type == PORT_ALTR_16550_F128)) && (port->fifosize > 1)) {
/* Bounds checking of TX threshold (valid 0 to fifosize-2) */
if ((up->tx_loadsz < 2) || (up->tx_loadsz > port->fifosize)) {
pr_err("ttyS%d TX FIFO Threshold errors, skipping\n",
serial_index(port));
} else {
serial_port_out(port, UART_ALTR_AFR,
UART_ALTR_EN_TXFIFO_LW);
serial_port_out(port, UART_ALTR_TX_LOW,
port->fifosize - up->tx_loadsz);
port->handle_irq = serial8250_tx_threshold_handle_irq;
}
}
if (port->irq) {
unsigned char iir1;
/*

8
include/uapi/linux/serial_reg.h
View File

@ -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 */