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Subject[PATCH 14/15] tty: hvc: introduce the hv_ops.flush operation for hvc drivers
Date
Use .flush to wait for drivers to flush their console outside of
the spinlock, to reduce lock/irq latencies.

Flush the hvc console driver after each write, which can help
messages make it out to the console after a crash.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
drivers/tty/hvc/hvc_console.c | 35 +++++++++++++++++++++++++++++++++--
drivers/tty/hvc/hvc_console.h | 1 +
2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 6131d5084c42..5414c4a87bea 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -110,6 +110,29 @@ static struct hvc_struct *hvc_get_by_index(int index)
return hp;
}

+static int __hvc_flush(const struct hv_ops *ops, uint32_t vtermno, bool wait)
+{
+ if (wait)
+ might_sleep();
+
+ if (ops->flush)
+ return ops->flush(vtermno, wait);
+ return 0;
+}
+
+static int hvc_console_flush(const struct hv_ops *ops, uint32_t vtermno)
+{
+ return __hvc_flush(ops, vtermno, false);
+}
+
+/*
+ * Wait for the console to flush before writing more to it. This sleeps.
+ */
+static int hvc_flush(struct hvc_struct *hp)
+{
+ return __hvc_flush(hp->ops, hp->vtermno, true);
+}
+
/*
* Initial console vtermnos for console API usage prior to full console
* initialization. Any vty adapter outside this range will not have usable
@@ -155,8 +178,12 @@ static void hvc_console_print(struct console *co, const char *b,
if (r <= 0) {
/* throw away characters on error
* but spin in case of -EAGAIN */
- if (r != -EAGAIN)
+ if (r != -EAGAIN) {
i = 0;
+ } else {
+ hvc_console_flush(cons_ops[index],
+ vtermnos[index]);
+ }
} else if (r > 0) {
i -= r;
if (i > 0)
@@ -164,6 +191,7 @@ static void hvc_console_print(struct console *co, const char *b,
}
}
}
+ hvc_console_flush(cons_ops[index], vtermnos[index]);
}

static struct tty_driver *hvc_console_device(struct console *c, int *index)
@@ -513,8 +541,11 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count

spin_unlock_irqrestore(&hp->lock, flags);

- if (count)
+ if (count) {
+ if (hp->n_outbuf > 0)
+ hvc_flush(hp);
cond_resched();
+ }
}

/*
diff --git a/drivers/tty/hvc/hvc_console.h b/drivers/tty/hvc/hvc_console.h
index ea63090e013f..e9319954c832 100644
--- a/drivers/tty/hvc/hvc_console.h
+++ b/drivers/tty/hvc/hvc_console.h
@@ -54,6 +54,7 @@ struct hvc_struct {
struct hv_ops {
int (*get_chars)(uint32_t vtermno, char *buf, int count);
int (*put_chars)(uint32_t vtermno, const char *buf, int count);
+ int (*flush)(uint32_t vtermno, bool wait);

/* Callbacks for notification. Called in open, close and hangup */
int (*notifier_add)(struct hvc_struct *hp, int irq);
--
2.17.0
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