sc16is7xx: use kthread_worker for tx_work and irq

Convert workqueue usage to a real-time kworker.  The problem
with workqueues is that we cannot set real-time priorities on
our work and asynchronous reconfiguration can be blocked by
less important tasks.

We need kthread for the interrupt anyway and because we will
now be using single kthread for all TX-related operations we
can get rid of the port mutex.

Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index ea61a29..e6553d0 100644 (file)
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -303,7 +303,7 @@ struct sc16is7xx_devtype {
 
 struct sc16is7xx_one {
        struct uart_port                port;
-       struct work_struct              tx_work;
+       struct kthread_work             tx_work;
        struct work_struct              md_work;
 };
 
@@ -311,15 +311,18 @@ struct sc16is7xx_port {
        struct uart_driver              uart;
        struct sc16is7xx_devtype        *devtype;
        struct regmap                   *regmap;
-       struct mutex                    mutex;
        struct clk                      *clk;
 #ifdef CONFIG_GPIOLIB
        struct gpio_chip                gpio;
 #endif
        unsigned char                   buf[SC16IS7XX_FIFO_SIZE];
+       struct kthread_worker           kworker;
+       struct task_struct              *kworker_task;
+       struct kthread_work             irq_work;
        struct sc16is7xx_one            p[0];
 };
 
+#define to_sc16is7xx_port(p,e) ((container_of((p), struct sc16is7xx_port, e)))
 #define to_sc16is7xx_one(p,e)  ((container_of((p), struct sc16is7xx_one, e)))
 
 static u8 sc16is7xx_port_read(struct uart_port *port, u8 reg)
@@ -616,9 +619,7 @@ static void sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno)
                                               !!(msr & SC16IS7XX_MSR_CTS_BIT));
                        break;
                case SC16IS7XX_IIR_THRI_SRC:
-                       mutex_lock(&s->mutex);
                        sc16is7xx_handle_tx(port);
-                       mutex_unlock(&s->mutex);
                        break;
                default:
                        dev_err_ratelimited(port->dev,
@@ -629,25 +630,29 @@ static void sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno)
        } while (1);
 }
 
-static irqreturn_t sc16is7xx_ist(int irq, void *dev_id)
+static void sc16is7xx_ist(struct kthread_work *ws)
 {
-       struct sc16is7xx_port *s = (struct sc16is7xx_port *)dev_id;
+       struct sc16is7xx_port *s = to_sc16is7xx_port(ws, irq_work);
        int i;
 
        for (i = 0; i < s->uart.nr; ++i)
                sc16is7xx_port_irq(s, i);
+}
+
+static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
+{
+       struct sc16is7xx_port *s = (struct sc16is7xx_port *)dev_id;
+
+       queue_kthread_work(&s->kworker, &s->irq_work);
 
        return IRQ_HANDLED;
 }
 
-static void sc16is7xx_wq_proc(struct work_struct *ws)
+static void sc16is7xx_tx_proc(struct kthread_work *ws)
 {
        struct sc16is7xx_one *one = to_sc16is7xx_one(ws, tx_work);
-       struct sc16is7xx_port *s = dev_get_drvdata(one->port.dev);
 
-       mutex_lock(&s->mutex);
        sc16is7xx_handle_tx(&one->port);
-       mutex_unlock(&s->mutex);
 }
 
 static void sc16is7xx_stop_tx(struct uart_port* port)
@@ -669,6 +674,7 @@ static void sc16is7xx_stop_rx(struct uart_port* port)
 
 static void sc16is7xx_start_tx(struct uart_port *port)
 {
+       struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
        struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
        /* handle rs485 */
@@ -677,8 +683,7 @@ static void sc16is7xx_start_tx(struct uart_port *port)
                mdelay(port->rs485.delay_rts_before_send);
        }
 
-       if (!work_pending(&one->tx_work))
-               schedule_work(&one->tx_work);
+       queue_kthread_work(&s->kworker, &one->tx_work);
 }
 
 static unsigned int sc16is7xx_tx_empty(struct uart_port *port)
@@ -909,6 +914,8 @@ static int sc16is7xx_startup(struct uart_port *port)
 
 static void sc16is7xx_shutdown(struct uart_port *port)
 {
+       struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
+
        /* Disable all interrupts */
        sc16is7xx_port_write(port, SC16IS7XX_IER_REG, 0);
        /* Disable TX/RX */
@@ -919,6 +926,8 @@ static void sc16is7xx_shutdown(struct uart_port *port)
                              SC16IS7XX_EFCR_TXDISABLE_BIT);
 
        sc16is7xx_power(port, 0);
+
+       flush_kthread_worker(&s->kworker);
 }
 
 static const char *sc16is7xx_type(struct uart_port *port)
@@ -1036,6 +1045,7 @@ static int sc16is7xx_probe(struct device *dev,
                           struct sc16is7xx_devtype *devtype,
                           struct regmap *regmap, int irq, unsigned long flags)
 {
+       struct sched_param sched_param = { .sched_priority = MAX_RT_PRIO / 2 };
        unsigned long freq, *pfreq = dev_get_platdata(dev);
        int i, ret;
        struct sc16is7xx_port *s;
@@ -1077,6 +1087,16 @@ static int sc16is7xx_probe(struct device *dev,
                goto out_clk;
        }
 
+       init_kthread_worker(&s->kworker);
+       init_kthread_work(&s->irq_work, sc16is7xx_ist);
+       s->kworker_task = kthread_run(kthread_worker_fn, &s->kworker,
+                                     "sc16is7xx");
+       if (IS_ERR(s->kworker_task)) {
+               ret = PTR_ERR(s->kworker_task);
+               goto out_uart;
+       }
+       sched_setscheduler(s->kworker_task, SCHED_FIFO, &sched_param);
+
 #ifdef CONFIG_GPIOLIB
        if (devtype->nr_gpio) {
                /* Setup GPIO cotroller */
@@ -1092,12 +1112,10 @@ static int sc16is7xx_probe(struct device *dev,
                s->gpio.can_sleep        = 1;
                ret = gpiochip_add(&s->gpio);
                if (ret)
-                       goto out_uart;
+                       goto out_thread;
        }
 #endif
 
-       mutex_init(&s->mutex);
-
        for (i = 0; i < devtype->nr_uart; ++i) {
                /* Initialize port data */
                s->p[i].port.line       = i;
@@ -1117,7 +1135,7 @@ static int sc16is7xx_probe(struct device *dev,
                                     SC16IS7XX_EFCR_RXDISABLE_BIT |
                                     SC16IS7XX_EFCR_TXDISABLE_BIT);
                /* Initialize queue for start TX */
-               INIT_WORK(&s->p[i].tx_work, sc16is7xx_wq_proc);
+               init_kthread_work(&s->p[i].tx_work, sc16is7xx_tx_proc);
                /* Initialize queue for changing mode */
                INIT_WORK(&s->p[i].md_work, sc16is7xx_md_proc);
                /* Register port */
@@ -1127,22 +1145,23 @@ static int sc16is7xx_probe(struct device *dev,
        }
 
        /* Setup interrupt */
-       ret = devm_request_threaded_irq(dev, irq, NULL, sc16is7xx_ist,
-                                       IRQF_ONESHOT | flags, dev_name(dev), s);
+       ret = devm_request_irq(dev, irq, sc16is7xx_irq,
+                              IRQF_ONESHOT | flags, dev_name(dev), s);
        if (!ret)
                return 0;
 
        for (i = 0; i < s->uart.nr; i++)
                uart_remove_one_port(&s->uart, &s->p[i].port);
 
-       mutex_destroy(&s->mutex);
-
 #ifdef CONFIG_GPIOLIB
        if (devtype->nr_gpio)
                gpiochip_remove(&s->gpio);
 
-out_uart:
+out_thread:
 #endif
+       kthread_stop(s->kworker_task);
+
+out_uart:
        uart_unregister_driver(&s->uart);
 
 out_clk:
@@ -1163,13 +1182,14 @@ static int sc16is7xx_remove(struct device *dev)
 #endif
 
        for (i = 0; i < s->uart.nr; i++) {
-               cancel_work_sync(&s->p[i].tx_work);
                cancel_work_sync(&s->p[i].md_work);
                uart_remove_one_port(&s->uart, &s->p[i].port);
                sc16is7xx_power(&s->p[i].port, 0);
        }
 
-       mutex_destroy(&s->mutex);
+       flush_kthread_worker(&s->kworker);
+       kthread_stop(s->kworker_task);
+
        uart_unregister_driver(&s->uart);
        if (!IS_ERR(s->clk))
                clk_disable_unprepare(s->clk);