On Thu, 2018-03-15 at 10:02 +1300, Joshua Scott wrote:
> 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.
>
Yep, something like this.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Couple of minor comments below.
> 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);
I would still define tries inside the function in a way how it's done in
_check_lcr().
> +
> + 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;
> + }
> +
Redundant empty string, and perhaps you don't need curly braces for now.
> } 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);
--
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy
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