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Subject[090/102] hvc_console: Improve tty/console put_chars handling
3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>

commit 8c2381af0d3ef62a681dac5a141b6dabb27bf2e1 upstream.

Currently, the hvc_console_print() function drops console output if the
hvc backend's put_chars() returns 0. This patch changes this behavior
to allow a retry through returning -EAGAIN.

This change also affects the hvc_push() function. Both functions are
changed to handle -EAGAIN and to retry the put_chars() operation.

If a hvc backend returns -EAGAIN, the retry handling differs:

- hvc_console_print() spins to write the complete console output.
- hvc_push() behaves the same way as for returning 0.

Now hvc backends can indirectly control the way how console output is
handled through the hvc console layer.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/tty/hvc/hvc_console.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -163,8 +163,10 @@ static void hvc_console_print(struct con
} else {
r = cons_ops[index]->put_chars(vtermnos[index], c, i);
if (r <= 0) {
- /* throw away chars on error */
- i = 0;
+ /* throw away characters on error
+ * but spin in case of -EAGAIN */
+ if (r != -EAGAIN)
+ i = 0;
} else if (r > 0) {
i -= r;
if (i > 0)
@@ -448,7 +450,7 @@ static int hvc_push(struct hvc_struct *h

n = hp->ops->put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
if (n <= 0) {
- if (n == 0) {
+ if (n == 0 || n == -EAGAIN) {
hp->do_wakeup = 1;
return 0;
}



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