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authorThor Thayer <tthayer@opensource.altera.com>2016-09-22 14:56:16 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-09-27 12:55:50 +0200
commit8e5470c9839caff94fe334e67ff7e7ace587282a (patch)
treed96d839061310f9c2e94f7fc24fc906d338f4d01 /drivers/tty
parentffea043965e4634617485b4d313d6c0099d817f0 (diff)
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>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/serial/8250/8250_port.c43
1 files changed, 43 insertions, 0 deletions
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 28d29fac1973..1bfb6fdbaa20 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -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;
/*