i2c: at91: fix SMBus quick command

The driver claims to support SMBus quick command but it was not the
case. This patch fixes this issue. Without it, i2cdetect finds imaginary
devices. And with some IP versions, trying to send 0 byte can cause
issue when writing data to an EEPROM.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

[wsa: improved the commit message]

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index aa59a254be2c..c02bf208084f 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -39,6 +39,7 @@
 #define AT91_TWI_STOP           0x0002  /* Send a Stop Condition */
 #define AT91_TWI_MSEN           0x0004  /* Master Transfer Enable */
 #define AT91_TWI_SVDIS          0x0020  /* Slave Transfer Disable */
+#define AT91_TWI_QUICK          0x0040  /* SMBus quick command */
 #define AT91_TWI_SWRST          0x0080  /* Software Reset */
 
 #define AT91_TWI_MMR            0x0004  /* Master Mode Register */
@@ -212,7 +213,11 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
 
         INIT_COMPLETION(dev->cmd_complete);
         dev->transfer_status = 0;
-        if (dev->msg->flags & I2C_M_RD) {
+
+        if (!dev->buf_len) {
+                at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_QUICK);
+                at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP);
+        } else if (dev->msg->flags & I2C_M_RD) {
                 unsigned start_flags = AT91_TWI_START;
 
                 if (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY) {