[Kgdb-bugreport] [PATCH 7/7] serial: kgdb_nmi: Replace hrtimer with irq_work ping

[Sumit Garg]

From: Daniel Thompson <daniel.thomp...@linaro.org>

Currently kgdb_nmi relies on a 100Hz timer to "defer" work from an NMI
handler. This is essentially doing the job that irq_work is designed to
do but in an odd and inefficient manner. Remove the timer code and
replace it with more appropriate irq_work related APIs.

Signed-off-by: Daniel Thompson <daniel.thomp...@linaro.org>
Signed-off-by: Sumit Garg <sumit.g...@linaro.org>
---
 drivers/tty/serial/kgdb_nmi.c | 35 ++++++++++-------------------------
 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c
index 2580f39..ad84eef 100644
--- a/drivers/tty/serial/kgdb_nmi.c
+++ b/drivers/tty/serial/kgdb_nmi.c
@@ -21,7 +21,7 @@
 #include <linux/tty_flip.h>
 #include <linux/serial_core.h>
 #include <linux/interrupt.h>
-#include <linux/hrtimer.h>
+#include <linux/irq_work.h>
 #include <linux/tick.h>
 #include <linux/kfifo.h>
 #include <linux/kgdb.h>
@@ -127,7 +127,7 @@ static struct console kgdb_nmi_console = {
 
 struct kgdb_nmi_tty_priv {
        struct tty_port port;
-       struct timer_list timer;
+       struct irq_work work;
        STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
 };
 
@@ -141,13 +141,12 @@ static void kgdb_tty_recv(int ch)
        if (!kgdb_nmi_port || ch < 0)
                return;
        /*
-        * Can't use port->tty->driver_data as tty might be not there. Timer
-        * will check for tty and will get the ref, but here we don't have to
-        * do that, and actually, we can't: we're in NMI context, no locks are
-        * possible.
+        * Can't use port->tty->driver_data as tty might be not there. Also, we
+        * can't even do that as we're in NMI context, no locks are possible.
         */
        priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);
        kfifo_in(&priv->fifo, &c, 1);
+       irq_work_queue(&priv->work);
 }
 
 static int kgdb_nmi_poll_one_knock(void)
@@ -222,18 +221,12 @@ bool kgdb_nmi_poll_knock(void)
        return true;
 }
 
-/*
- * The tasklet is cheap, it does not cause wakeups when reschedules itself,
- * instead it waits for the next tick.
- */
-static void kgdb_nmi_tty_receiver(struct timer_list *t)
+static void kgdb_nmi_tty_receiver(struct irq_work *work)
 {
-       struct kgdb_nmi_tty_priv *priv = from_timer(priv, t, timer);
+       struct kgdb_nmi_tty_priv *priv =
+           container_of(work, struct kgdb_nmi_tty_priv, work);
        char ch;
 
-       priv->timer.expires = jiffies + (HZ/100);
-       add_timer(&priv->timer);
-
        if (likely(!atomic_read(&kgdb_nmi_num_readers) ||
                   !kfifo_len(&priv->fifo)))
                return;
@@ -245,22 +238,13 @@ static void kgdb_nmi_tty_receiver(struct timer_list *t)
 
 static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
 {
-       struct kgdb_nmi_tty_priv *priv =
-           container_of(port, struct kgdb_nmi_tty_priv, port);
-
        kgdb_nmi_port = port;
-       priv->timer.expires = jiffies + (HZ/100);
-       add_timer(&priv->timer);
 
        return 0;
 }
 
 static void kgdb_nmi_tty_shutdown(struct tty_port *port)
 {
-       struct kgdb_nmi_tty_priv *priv =
-           container_of(port, struct kgdb_nmi_tty_priv, port);
-
-       del_timer(&priv->timer);
        kgdb_nmi_port = NULL;
 }
 
@@ -279,7 +263,8 @@ static int kgdb_nmi_tty_install(struct tty_driver *drv, 
struct tty_struct *tty)
                return -ENOMEM;
 
        INIT_KFIFO(priv->fifo);
-       timer_setup(&priv->timer, kgdb_nmi_tty_receiver, 0);
+       init_irq_work(&priv->work, kgdb_nmi_tty_receiver);
+       atomic_set(&priv->work.flags, IRQ_WORK_LAZY);
        tty_port_init(&priv->port);
        priv->port.ops = &kgdb_nmi_tty_port_ops;
        tty->driver_data = priv;
-- 
2.7.4



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