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>

1 files changed, 24 insertions, 21 deletions

diff --git a/drivers/i2c/busses/i2c-taos-evm.c b/drivers/i2c/busses/i2c-taos-evm.c
index 224aa12ee7c8..dd39c1eb03ed 100644
--- 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;