diff options
Diffstat (limited to 'drivers/tty/serial/8250/8250_aspeed_vuart.c')
| -rw-r--r-- | drivers/tty/serial/8250/8250_aspeed_vuart.c | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c index 74a408d9db24..435bec40dee6 100644 --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c @@ -10,6 +10,8 @@ #include <linux/of_address.h> #include <linux/of_irq.h> #include <linux/of_platform.h> +#include <linux/tty.h> +#include <linux/tty_flip.h> #include <linux/clk.h> #include "8250.h" @@ -28,9 +30,18 @@ struct aspeed_vuart { void __iomem *regs; struct clk *clk; int line; + struct timer_list unthrottle_timer; + struct uart_8250_port *port; }; /* + * If we fill the tty flip buffers, we throttle the data ready interrupt + * to prevent dropped characters. This timeout defines how long we wait + * to (conditionally, depending on buffer state) unthrottle. + */ +static const int unthrottle_timeout = HZ/10; + +/* * The VUART is basically two UART 'front ends' connected by their FIFO * (no actual serial line in between). One is on the BMC side (management * controller) and one is on the host CPU side. @@ -179,6 +190,114 @@ static void aspeed_vuart_shutdown(struct uart_port *uart_port) serial8250_do_shutdown(uart_port); } +static void __aspeed_vuart_set_throttle(struct uart_8250_port *up, + bool throttle) +{ + unsigned char irqs = UART_IER_RLSI | UART_IER_RDI; + + up->ier &= ~irqs; + if (!throttle) + up->ier |= irqs; + serial_out(up, UART_IER, up->ier); +} +static void aspeed_vuart_set_throttle(struct uart_port *port, bool throttle) +{ + struct uart_8250_port *up = up_to_u8250p(port); + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + __aspeed_vuart_set_throttle(up, throttle); + spin_unlock_irqrestore(&port->lock, flags); +} + +static void aspeed_vuart_throttle(struct uart_port *port) +{ + aspeed_vuart_set_throttle(port, true); +} + +static void aspeed_vuart_unthrottle(struct uart_port *port) +{ + aspeed_vuart_set_throttle(port, false); +} + +static void aspeed_vuart_unthrottle_exp(struct timer_list *timer) +{ + struct aspeed_vuart *vuart = from_timer(vuart, timer, unthrottle_timer); + struct uart_8250_port *up = vuart->port; + + if (!tty_buffer_space_avail(&up->port.state->port)) { + mod_timer(&vuart->unthrottle_timer, + jiffies + unthrottle_timeout); + return; + } + + aspeed_vuart_unthrottle(&up->port); +} + +/* + * Custom interrupt handler to manage finer-grained flow control. Although we + * have throttle/unthrottle callbacks, we've seen that the VUART device can + * deliver characters faster than the ldisc has a chance to check buffer space + * against the throttle threshold. This results in dropped characters before + * the throttle. + * + * We do this by checking for flip buffer space before RX. If we have no space, + * throttle now and schedule an unthrottle for later, once the ldisc has had + * a chance to drain the buffers. + */ +static int aspeed_vuart_handle_irq(struct uart_port *port) +{ + struct uart_8250_port *up = up_to_u8250p(port); + unsigned int iir, lsr; + unsigned long flags; + int space, count; + + iir = serial_port_in(port, UART_IIR); + + if (iir & UART_IIR_NO_INT) + return 0; + + spin_lock_irqsave(&port->lock, flags); + + lsr = serial_port_in(port, UART_LSR); + + if (lsr & (UART_LSR_DR | UART_LSR_BI)) { + space = tty_buffer_space_avail(&port->state->port); + + if (!space) { + /* throttle and schedule an unthrottle later */ + struct aspeed_vuart *vuart = port->private_data; + __aspeed_vuart_set_throttle(up, true); + + if (!timer_pending(&vuart->unthrottle_timer)) { + vuart->port = up; + mod_timer(&vuart->unthrottle_timer, + jiffies + unthrottle_timeout); + } + + } else { + count = min(space, 256); + + do { + serial8250_read_char(up, lsr); + lsr = serial_in(up, UART_LSR); + if (--count == 0) + break; + } while (lsr & (UART_LSR_DR | UART_LSR_BI)); + + tty_flip_buffer_push(&port->state->port); + } + } + + serial8250_modem_status(up); + if (lsr & UART_LSR_THRE) + serial8250_tx_chars(up); + + spin_unlock_irqrestore(&port->lock, flags); + + return 1; +} + static int aspeed_vuart_probe(struct platform_device *pdev) { struct uart_8250_port port; @@ -195,6 +314,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) return -ENOMEM; vuart->dev = &pdev->dev; + timer_setup(&vuart->unthrottle_timer, aspeed_vuart_unthrottle_exp, 0); res = platform_get_resource(pdev, IORESOURCE_MEM, 0); vuart->regs = devm_ioremap_resource(&pdev->dev, res); @@ -208,6 +328,9 @@ static int aspeed_vuart_probe(struct platform_device *pdev) port.port.mapsize = resource_size(res); port.port.startup = aspeed_vuart_startup; port.port.shutdown = aspeed_vuart_shutdown; + port.port.throttle = aspeed_vuart_throttle; + port.port.unthrottle = aspeed_vuart_unthrottle; + port.port.status = UPSTAT_SYNC_FIFO; port.port.dev = &pdev->dev; rc = sysfs_create_group(&vuart->dev->kobj, &aspeed_vuart_attr_group); @@ -253,6 +376,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) port.port.irq = irq_of_parse_and_map(np, 0); port.port.irqflags = IRQF_SHARED; + port.port.handle_irq = aspeed_vuart_handle_irq; port.port.iotype = UPIO_MEM; port.port.type = PORT_16550A; port.port.uartclk = clk; @@ -292,6 +416,7 @@ static int aspeed_vuart_remove(struct platform_device *pdev) { struct aspeed_vuart *vuart = platform_get_drvdata(pdev); + del_timer_sync(&vuart->unthrottle_timer); aspeed_vuart_set_enabled(vuart, false); serial8250_unregister_port(vuart->line); sysfs_remove_group(&vuart->dev->kobj, &aspeed_vuart_attr_group); |