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

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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>
This commit is contained in:
Jean Delvare 2009-09-18 22:45:43 +02:00
parent 6a891a3111
commit 27693ce5f3
1 changed files with 24 additions and 21 deletions
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45
drivers/i2c/busses/i2c-taos-evm.c
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@ -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;