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path: root/drivers/tty/hvc/hvc_console.c
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Diffstat (limited to 'drivers/tty/hvc/hvc_console.c')
-rw-r--r--drivers/tty/hvc/hvc_console.c38
1 files changed, 33 insertions, 5 deletions
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 5414c4a87bea..27284a2dcd2b 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -522,6 +522,8 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
return -EIO;
while (count > 0) {
+ int ret = 0;
+
spin_lock_irqsave(&hp->lock, flags);
rsize = hp->outbuf_size - hp->n_outbuf;
@@ -537,10 +539,13 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
}
if (hp->n_outbuf > 0)
- hvc_push(hp);
+ ret = hvc_push(hp);
spin_unlock_irqrestore(&hp->lock, flags);
+ if (!ret)
+ break;
+
if (count) {
if (hp->n_outbuf > 0)
hvc_flush(hp);
@@ -623,6 +628,15 @@ static int hvc_chars_in_buffer(struct tty_struct *tty)
#define MAX_TIMEOUT (2000)
static u32 timeout = MIN_TIMEOUT;
+/*
+ * Maximum number of bytes to get from the console driver if hvc_poll is
+ * called from driver (and can't sleep). Any more than this and we break
+ * and start polling with khvcd. This value was derived from from an OpenBMC
+ * console with the OPAL driver that results in about 0.25ms interrupts off
+ * latency.
+ */
+#define HVC_ATOMIC_READ_MAX 128
+
#define HVC_POLL_READ 0x00000001
#define HVC_POLL_WRITE 0x00000002
@@ -669,8 +683,8 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
if (!hp->irq_requested)
poll_mask |= HVC_POLL_READ;
+ read_again:
/* Read data if any */
-
count = tty_buffer_request_room(&hp->port, N_INBUF);
/* If flip is full, just reschedule a later read */
@@ -717,9 +731,23 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
#endif /* CONFIG_MAGIC_SYSRQ */
tty_insert_flip_char(&hp->port, buf[i], 0);
}
- if (n == count)
- poll_mask |= HVC_POLL_READ;
- read_total = n;
+ read_total += n;
+
+ if (may_sleep) {
+ /* Keep going until the flip is full */
+ spin_unlock_irqrestore(&hp->lock, flags);
+ cond_resched();
+ spin_lock_irqsave(&hp->lock, flags);
+ goto read_again;
+ } else if (read_total < HVC_ATOMIC_READ_MAX) {
+ /* Break and defer if it's a large read in atomic */
+ goto read_again;
+ }
+
+ /*
+ * Latency break, schedule another poll immediately.
+ */
+ poll_mask |= HVC_POLL_READ;
out:
/* Wakeup write queue if necessary */
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