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

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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@alliedtelesis.co.nz>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Joshua Scott 2018-03-16 13:42:00 +13:00 • committed by Greg Kroah-Hartman
parent 63ba1e00f1
commit b7639b0b15
2 changed files with 29 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

4
arch/arm/boot/dts/armada-38x.dtsi
View file

@ -163,7 +163,7 @@
}; };
uart0: serial@12000 { uart0: serial@12000 {
compatible = "snps,dw-apb-uart"; compatible = "marvell,armada-38x-uart";
reg = <0x12000 0x100>; reg = <0x12000 0x100>;
reg-shift = <2>; reg-shift = <2>;
interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>; interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
@ -173,7 +173,7 @@
}; };
uart1: serial@12100 { uart1: serial@12100 {
compatible = "snps,dw-apb-uart"; compatible = "marvell,armada-38x-uart";
reg = <0x12100 0x100>; reg = <0x12100 0x100>;
reg-shift = <2>; reg-shift = <2>;
interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>; interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;

31
drivers/tty/serial/8250/8250_dw.c
View file

@ -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 */ /* 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; unsigned int lsr;
while (tries--) { while (tries--) {
lsr = readb (p->membase + (UART_LSR << p->regshift)); lsr = readb (p->membase + (UART_LSR << p->regshift));
if (lsr & UART_LSR_TEMT) if (lsr & UART_LSR_TEMT)
break; 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; struct dw8250_data *d = p->private_data;
/* Allow the TX to drain before we reconfigure */ /* Allow the TX to drain before we reconfigure */
if (offset == UART_LCR) 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)); 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_in = dw8250_serial_in32be;
p->serial_out = dw8250_serial_out32be; 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)) { } else if (acpi_dev_present("APMC0D08", NULL, -1)) {
p->iotype = UPIO_MEM32; p->iotype = UPIO_MEM32;
p->regshift = 2; 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[] = { static const struct of_device_id dw8250_of_match[] = {
{ .compatible = "snps,dw-apb-uart" }, { .compatible = "snps,dw-apb-uart" },
{ .compatible = "cavium,octeon-3860-uart" }, { .compatible = "cavium,octeon-3860-uart" },
{ .compatible = "marvell,armada-38x-uart" },
{ /* Sentinel */ } { /* Sentinel */ }
}; };
MODULE_DEVICE_TABLE(of, dw8250_of_match); MODULE_DEVICE_TABLE(of, dw8250_of_match);