The previous implementation has had a detrimental effect on devices using
high bitrates (bluetooth), as the fifo being non-empty for a single check
would result in a 10 µs delay.
Limit the change to devices with the new "marvell,armada-38x-uart"
compatible string. Also update the code to allow the first 1000 retries
to not perform a delay.
The maximum duration of retries has been increased to cover a worst-case
seen on the Armada 385 SoC. "dmesg ; resize", will fill the buffer with
text to output before doing a resize. At 9600 baud this took up to 13 ms
to flush all characters and avoid some getting lost.
Signed-off-by: Joshua Scott <joshua.scott@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
Re-sending with Andy's review tag added.
Changes since v1:
Moved 'tries' value into dw82_tx_wait_empty
Removed curly braces around one-line if case
Updated to latest tty-next code
arch/arm/boot/dts/armada-38x.dtsi | 4 ++--
drivers/tty/serial/8250/8250_dw.c | 31 +++++++++++++++++++++++++++----
2 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/arch/arm/boot/dts/armada-38x.dtsi b/arch/arm/boot/dts/armada-38x.dtsi
index a6cc568f74f7..73553ccad900 100644
--- a/arch/arm/boot/dts/armada-38x.dtsi
+++ b/arch/arm/boot/dts/armada-38x.dtsi
@@ -200,7 +200,7 @@
};
uart0: serial@12000 {
- compatible = "snps,dw-apb-uart";
+ compatible = "marvell,armada-38x-uart";
reg = <0x12000 0x100>;
reg-shift = <2>;
interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
@@ -210,7 +210,7 @@
};
uart1: serial@12100 {
- compatible = "snps,dw-apb-uart";
+ compatible = "marvell,armada-38x-uart";
reg = <0x12100 0x100>;
reg-shift = <2>;
interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 6fcdb90f616a..0529b5cc094b 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -121,25 +121,44 @@ static void dw8250_check_lcr(struct uart_port *p, int value)
}
/* Returns once the transmitter is empty or we run out of retries */
-static void dw8250_tx_wait_empty(struct uart_port *p, int tries)
+static void dw8250_tx_wait_empty(struct uart_port *p)
{
+ unsigned int tries = 20000;
+ unsigned int delay_threshold = tries - 1000;
unsigned int lsr;
while (tries--) {
lsr = readb (p->membase + (UART_LSR << p->regshift));
if (lsr & UART_LSR_TEMT)
break;
- udelay (10);
+
+ /* The device is first given a chance to empty without delay,
+ * to avoid slowdowns at high bitrates. If after 1000 tries
+ * the buffer has still not emptied, allow more time for low-
+ * speed links. */
+ if (tries < delay_threshold)
+ udelay (1);
}
}
-static void dw8250_serial_out(struct uart_port *p, int offset, int value)
+static void dw8250_serial_out38x(struct uart_port *p, int offset, int value)
{
struct dw8250_data *d = p->private_data;
/* Allow the TX to drain before we reconfigure */
if (offset == UART_LCR)
- dw8250_tx_wait_empty(p, 1000);
+ dw8250_tx_wait_empty(p);
+
+ writeb(value, p->membase + (offset << p->regshift));
+
+ if (offset == UART_LCR && !d->uart_16550_compatible)
+ dw8250_check_lcr(p, value);
+}
+
+
+static void dw8250_serial_out(struct uart_port *p, int offset, int value)
+{
+ struct dw8250_data *d = p->private_data;
writeb(value, p->membase + (offset << p->regshift));
@@ -357,6 +376,9 @@ static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data)
p->serial_in = dw8250_serial_in32be;
p->serial_out = dw8250_serial_out32be;
}
+ if (of_device_is_compatible(np, "marvell,armada-38x-uart"))
+ p->serial_out = dw8250_serial_out38x;
+
} else if (acpi_dev_present("APMC0D08", NULL, -1)) {
p->iotype = UPIO_MEM32;
p->regshift = 2;
@@ -666,6 +688,7 @@ static const struct dev_pm_ops dw8250_pm_ops = {
static const struct of_device_id dw8250_of_match[] = {
{ .compatible = "snps,dw-apb-uart" },
{ .compatible = "cavium,octeon-3860-uart" },
+ { .compatible = "marvell,armada-38x-uart" },
{ /* Sentinel */ }
};
MODULE_DEVICE_TABLE(of, dw8250_of_match);
--
2.16.2
--
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