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Commit b7639b0b authored by Joshua Scott's avatar Joshua Scott Committed by Greg Kroah-Hartman
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serial: 8250_dw: Limit dw8250_tx_wait_empty quirk to armada-38x devices 



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: default avatarJoshua Scott <joshua.scott@alliedtelesis.co.nz>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 63ba1e00

arch/arm/boot/dts/armada-38x.dtsi

+2 −2
Original line number Diff line number Diff line
@@ -163,7 +163,7 @@ 
			};



			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>;
@@ -173,7 +173,7 @@ 
			};



			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>;

drivers/tty/serial/8250/8250_dw.c

+27 −4
Original line number Diff line number Diff line
@@ -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);