i2c-taos-evm: Switch echo off to improve performance

When echo is on, we waste time reading back our orders. Switching echo
off makes performance much better: SMBus byte data transactions are 47%
faster and byte transactions are 24% faster.

Signed-off-by: Jean Delvare <khali@linux-fr.org>

diff --git a/drivers/i2c/busses/i2c-taos-evm.c b/drivers/i2c/busses/i2c-taos-evm.c
index 224aa12..dd39c1e 100644 (file)
--- a/drivers/i2c/busses/i2c-taos-evm.c
+++ b/drivers/i2c/busses/i2c-taos-evm.c
@@ -32,10 +32,12 @@
 
 #define TAOS_STATE_INIT                0
 #define TAOS_STATE_IDLE                1
-#define TAOS_STATE_SEND                2
+#define TAOS_STATE_EOFF                2
 #define TAOS_STATE_RECV                3
 
 #define TAOS_CMD_RESET         0x12
+#define TAOS_CMD_ECHO_ON       '+'
+#define TAOS_CMD_ECHO_OFF      '-'
 
 static DECLARE_WAIT_QUEUE_HEAD(wq);
 
@@ -102,17 +104,9 @@ static int taos_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 
        /* Send the transaction to the TAOS EVM */
        dev_dbg(&adapter->dev, "Command buffer: %s\n", taos->buffer);
-       taos->pos = 0;
-       taos->state = TAOS_STATE_SEND;
-       serio_write(serio, taos->buffer[0]);
-       wait_event_interruptible_timeout(wq, taos->state == TAOS_STATE_IDLE,
-                                        msecs_to_jiffies(250));
-       if (taos->state != TAOS_STATE_IDLE) {
-               dev_err(&adapter->dev, "Transaction failed "
-                       "(state=%d, pos=%d)\n", taos->state, taos->pos);
-               taos->addr = 0;
-               return -EIO;
-       }
+       for (p = taos->buffer; *p; p++)
+               serio_write(serio, *p);
+
        taos->addr = addr;
 
        /* Start the transaction and read the answer */
@@ -122,7 +116,7 @@ static int taos_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
        wait_event_interruptible_timeout(wq, taos->state == TAOS_STATE_IDLE,
                                         msecs_to_jiffies(150));
        if (taos->state != TAOS_STATE_IDLE
-        || taos->pos != 6) {
+        || taos->pos != 5) {
                dev_err(&adapter->dev, "Transaction timeout (pos=%d)\n",
                        taos->pos);
                return -EIO;
@@ -130,7 +124,7 @@ static int taos_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
        dev_dbg(&adapter->dev, "Answer buffer: %s\n", taos->buffer);
 
        /* Interpret the returned string */
-       p = taos->buffer + 2;
+       p = taos->buffer + 1;
        p[3] = '\0';
        if (!strcmp(p, "NAK"))
                return -ENODEV;
@@ -173,13 +167,9 @@ static irqreturn_t taos_interrupt(struct serio *serio, unsigned char data,
                        wake_up_interruptible(&wq);
                }
                break;
-       case TAOS_STATE_SEND:
-               if (taos->buffer[++taos->pos])
-                       serio_write(serio, taos->buffer[taos->pos]);
-               else {
-                       taos->state = TAOS_STATE_IDLE;
-                       wake_up_interruptible(&wq);
-               }
+       case TAOS_STATE_EOFF:
+               taos->state = TAOS_STATE_IDLE;
+               wake_up_interruptible(&wq);
                break;
        case TAOS_STATE_RECV:
                taos->buffer[taos->pos++] = data;
@@ -257,6 +247,19 @@ static int taos_connect(struct serio *serio, struct serio_driver *drv)
        }
        strlcpy(adapter->name, name, sizeof(adapter->name));
 
+       /* Turn echo off for better performance */
+       taos->state = TAOS_STATE_EOFF;
+       serio_write(serio, TAOS_CMD_ECHO_OFF);
+
+       wait_event_interruptible_timeout(wq, taos->state == TAOS_STATE_IDLE,
+                                        msecs_to_jiffies(250));
+       if (taos->state != TAOS_STATE_IDLE) {
+               err = -ENODEV;
+               dev_err(&adapter->dev, "Echo off failed "
+                       "(state=%d)\n", taos->state);
+               goto exit_close;
+       }
+
        err = i2c_add_adapter(adapter);
        if (err)
                goto exit_close;