Switch RX processing from tasklet to (delayed) work queue. This allows
receiver more room to process incoming data and prevents flood of
"ttyGS0: RX not scheduled?" messages on HS receive on slow CPU.
A side effect is 2.4MB/s zmodem transfer speed (up from 1.8MB/s)
on my test board.
Signed-off-by: Michał Mirosław <mirq-linux@xxxxxxxxxxxx>
---
* against v4.19.9
---
drivers/usb/gadget/function/u_serial.c | 35 +++++++++++---------------
1 file changed, 14 insertions(+), 21 deletions(-)
diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 29436f75bbe0..65f634ec7fc2 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -16,7 +16,6 @@
#include <linux/kernel.h>
#include <linux/sched.h>
-#include <linux/interrupt.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/tty.h>
@@ -26,6 +25,7 @@
#include <linux/module.h>
#include <linux/console.h>
#include <linux/kthread.h>
+#include <linux/workqueue.h>
#include <linux/kfifo.h>
#include "u_serial.h"
@@ -110,7 +110,7 @@ struct gs_port {
int read_allocated;
struct list_head read_queue;
unsigned n_read;
- struct tasklet_struct push;
+ struct delayed_work push;
struct list_head write_pool;
int write_started;
@@ -352,9 +352,10 @@ __acquires(&port->port_lock)
* So QUEUE_SIZE packets plus however many the FIFO holds (usually two)
* can be buffered before the TTY layer's buffers (currently 64 KB).
*/
-static void gs_rx_push(unsigned long _port)
+static void gs_rx_push(struct work_struct *work)
{
- struct gs_port *port = (void *)_port;
+ struct delayed_work *w = to_delayed_work(work);
+ struct gs_port *port = container_of(w, struct gs_port, push);
struct tty_struct *tty;
struct list_head *queue = &port->read_queue;
bool disconnect = false;
@@ -429,21 +430,13 @@ static void gs_rx_push(unsigned long _port)
/* We want our data queue to become empty ASAP, keeping data
* in the tty and ldisc (not here). If we couldn't push any
- * this time around, there may be trouble unless there's an
- * implicit tty_unthrottle() call on its way...
+ * this time around, RX may be starved, so wait until next jiffy.
*
- * REVISIT we should probably add a timer to keep the tasklet
- * from starving ... but it's not clear that case ever happens.
+ * We may leave non-empty queue only when there is a tty, and
+ * either it is throttled or there is no more room in flip buffer.
*/
- if (!list_empty(queue) && tty) {
- if (!tty_throttled(tty)) {
- if (do_push)
- tasklet_schedule(&port->push);
- else
- pr_warn("ttyGS%d: RX not scheduled?\n",
- port->port_num);
- }
- }
+ if (!list_empty(queue) && !tty_throttled(tty))
+ schedule_delayed_work(&port->push, 1);
/* If we're still connected, refill the USB RX queue. */
if (!disconnect && port->port_usb)
@@ -459,7 +452,7 @@ static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
/* Queue all received data until the tty layer is ready for it. */
spin_lock(&port->port_lock);
list_add_tail(&req->list, &port->read_queue);
- tasklet_schedule(&port->push);
+ schedule_delayed_work(&port->push, 0);
spin_unlock(&port->port_lock);
}
@@ -854,8 +847,8 @@ static void gs_unthrottle(struct tty_struct *tty)
* rts/cts, or other handshaking with the host, but if the
* read queue backs up enough we'll be NAKing OUT packets.
*/
- tasklet_schedule(&port->push);
pr_vdebug("ttyGS%d: unthrottle\n", port->port_num);
+ schedule_delayed_work(&port->push, 0);
}
spin_unlock_irqrestore(&port->port_lock, flags);
}
@@ -1159,7 +1152,7 @@ gs_port_alloc(unsigned port_num, struct usb_cdc_line_coding *coding)
init_waitqueue_head(&port->drain_wait);
init_waitqueue_head(&port->close_wait);
- tasklet_init(&port->push, gs_rx_push, (unsigned long) port);
+ INIT_DELAYED_WORK(&port->push, gs_rx_push);
INIT_LIST_HEAD(&port->read_pool);
INIT_LIST_HEAD(&port->read_queue);
@@ -1186,7 +1179,7 @@ static int gs_closed(struct gs_port *port)
static void gserial_free_port(struct gs_port *port)
{
- tasklet_kill(&port->push);
+ cancel_delayed_work_sync(&port->push);
/* wait for old opens to finish */
wait_event(port->close_wait, gs_closed(port));
WARN_ON(port->port_usb != NULL);
--
2.19.2
