[PATCH v1 19/19] hid-ft260: uart: improve write performance

[Michael Zaidman <michael.zaidman@gmail.com>]

Tx performance with the current buffer size of 256 bytes is lower when
the data length exceeds the xmit buf size.

[134331.147978] ft260_uart_write: count: 288, len: 256
[134331.157945] ft260_uart_write: count: 32, len: 32
[134331.159977] ft260_uart_write: count: 288, len: 256
[134331.169990] ft260_uart_write: count: 32, len: 32

1. Increase the xmit buffer size to page size as used in the serial core
and other tty drivers.

2. Remove the xmit buffer fulness against the watermark checking and the
tty_wakeup calling in the ft260_uart_transmit_chars routine. This code is
taken from other drivers, but other drivers may call the routine from the
interrupt context. In our case, this condition is always True since xmit
buffer filling and emptying are serialized and done synchronously.

Tested with picocom ASCII file transfer by 288-byte chunks at 921600
bauds rate with above 20% performance improvement.

Before:
2821.7 Kbytes transferred at 47367 CPS... Done.

After:
2821.7 Kbytes transferred at 57788 CPS... Done.

Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
---
 drivers/hid/hid-ft260.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 6b172bfa4f98..1188b8e09938 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -308,8 +308,7 @@ enum {
 #define FT260_UART_EN_PW_SAVE_BAUD	(4800)
 
 #define UART_COUNT_MAX (4) /* Number of supported UARTs */
-#define XMIT_FIFO_SIZE (256)
-#define TTY_WAKEUP_WATERMARK (XMIT_FIFO_SIZE / 2)
+#define XMIT_FIFO_SIZE (PAGE_SIZE)
 
 static const struct hid_device_id ft260_devices[] = {
 	{ HID_USB_DEVICE(USB_VENDOR_ID_FUTURE_TECHNOLOGY,
@@ -1211,7 +1210,7 @@ static int ft260_uart_transmit_chars(struct ft260_device *port)
 
 		len = kfifo_out_spinlocked(xmit, rep->data, len, &port->xmit_fifo_lock);
 
-		ret = ft260_hid_output_report(hdev, (u8 *)rep, len + sizeof(*rep));
+		ret = ft260_hid_output_report(hdev, (u8 *)rep, len + 2);
 		if (ret < 0)
 			goto tty_out;
 
@@ -1219,10 +1218,6 @@ static int ft260_uart_transmit_chars(struct ft260_device *port)
 		port->icount.tx += len;
 	} while (data_len > 0);
 
-	len = kfifo_len(xmit);
-	if ((XMIT_FIFO_SIZE - len) > TTY_WAKEUP_WATERMARK)
-		tty_wakeup(tty);
-
 	ret = 0;
 
 tty_out:
@@ -1546,7 +1541,7 @@ static int ft260_uart_port_activate(struct tty_port *tport, struct tty_struct *t
 	if (baudrate > FT260_UART_EN_PW_SAVE_BAUD)
 		ft260_uart_wakeup_workaraund_enable(port, true);
 
-	ft260_dbg("configurd baudrate = %d", baudrate);
+	ft260_dbg("configured baudrate = %d", baudrate);
 
 	mod_timer(&port->wakeup_timer, jiffies +
 		  msecs_to_jiffies(FT260_WAKEUP_NEEDED_AFTER_MS));
-- 
2.40.1