[PATCH] serial: 8250_dw: Limit dw8250_tx_wait_empty quirk to armada-38x devices

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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>
---
 arch/arm/boot/dts/armada-38x.dtsi |  4 ++--
 drivers/tty/serial/8250/8250_dw.c | 30 +++++++++++++++++++++++++++---
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/arch/arm/boot/dts/armada-38x.dtsi b/arch/arm/boot/dts/armada-38x.dtsi
index 00ff549..4e6d8d6 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 823c1dc..9656707 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -127,23 +127,41 @@ 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)
 {
+	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, 20000);
+
+	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));
 
@@ -361,6 +379,11 @@ 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 (has_acpi_companion(p->dev)) {
 		const struct acpi_device_id *id;
 
@@ -675,6 +698,7 @@ 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

--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux PPP]     [Linux FS]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Linmodem]     [Device Mapper]     [Linux Kernel for ARM]

  Powered by Linux