@@ -161,6 +161,10 @@ static void dw8250_serial_out(struct uart_port *p, int offset, int value)
{
struct dw8250_data *d = to_dw8250_data(p->private_data);
+ /* Allow the TX to drain before we reconfigure */
+ if (offset == UART_LCR && d->drain_before_lcr_change)
+ dw8250_tx_wait_empty(p);
+
writeb(value, p->membase + (offset << p->regshift));
if (offset == UART_LCR && !d->uart_16550_compatible)
@@ -197,6 +201,10 @@ static void dw8250_serial_outq(struct uart_port *p, int offset, int value)
{
struct dw8250_data *d = to_dw8250_data(p->private_data);
+ /* Allow the TX to drain before we reconfigure */
+ if (offset == UART_LCR && d->drain_before_lcr_change)
+ dw8250_tx_wait_empty(p);
+
value &= 0xff;
__raw_writeq(value, p->membase + (offset << p->regshift));
/* Read back to ensure register write ordering. */
@@ -211,6 +219,10 @@ static void dw8250_serial_out32(struct uart_port *p, int offset, int value)
{
struct dw8250_data *d = to_dw8250_data(p->private_data);
+ /* Allow the TX to drain before we reconfigure */
+ if (offset == UART_LCR && d->drain_before_lcr_change)
+ dw8250_tx_wait_empty(p);
+
writel(value, p->membase + (offset << p->regshift));
if (offset == UART_LCR && !d->uart_16550_compatible)
@@ -228,6 +240,10 @@ static void dw8250_serial_out32be(struct uart_port *p, int offset, int value)
{
struct dw8250_data *d = to_dw8250_data(p->private_data);
+ /* Allow the TX to drain before we reconfigure */
+ if (offset == UART_LCR && d->drain_before_lcr_change)
+ dw8250_tx_wait_empty(p);
+
iowrite32be(value, p->membase + (offset << p->regshift));
if (offset == UART_LCR && !d->uart_16550_compatible)
@@ -597,6 +613,8 @@ static int dw8250_probe(struct platform_device *pdev)
/* Always ask for fixed clock rate from a property. */
device_property_read_u32(dev, "clock-frequency", &p->uartclk);
+ data->drain_before_lcr_change = device_property_read_bool(dev, "drain-before-lcr-change");
+
/* If there is separate baudclk, get the rate from it. */
data->clk = devm_clk_get_optional(dev, "baudclk");
if (data->clk == NULL)
@@ -45,6 +45,7 @@ struct dw8250_data {
unsigned int skip_autocfg:1;
unsigned int uart_16550_compatible:1;
+ unsigned int drain_before_lcr_change:1;
};
void dw8250_do_set_termios(struct uart_port *p, struct ktermios *termios, const struct ktermios *old);
Writes to UART_LCR can result in characters that are currently held in the TX FIFO being lost rather than sent, even if the userspace process has attempted to flush them. This is most visible when using the "resize" command (tested on Busybox), where we have observed the escape code for restoring cursor position becoming mangled. Since this appears to be a more common problem add a new driver option to flush the TX FIFO before writing to the UART_LCR. Signed-off-by: Richard Laing <richard.laing@alliedtelesis.co.nz> --- drivers/tty/serial/8250/8250_dw.c | 18 ++++++++++++++++++ drivers/tty/serial/8250/8250_dwlib.h | 1 + 2 files changed, 19 insertions(+)