Hello Grygorii, On Mon, Nov 24, 2014 at 03:34:35PM +0200, Grygorii Strashko wrote: > On 11/23/2014 10:33 PM, Uwe Kleine-König wrote: > > A call to .master_xfer with a message sequence implicitly expects ACKs > > from the slave and doesn't tell anything about what should be done on a > > NAK. So IMHO you must not send a P when the slave responds with a NAK, > > but error out and let the sender decide if it wants to reply with P or > > Sr. > > Sry, but what should be done is defined by I2C/SMbus specs? Does it? > For SMBus devices, the specification states (http://smbus.org/specs/) > "4.2.Acknowledge (ACK) and not acknowledge (NACK)": > - "The slave device detects an invalid command or invalid data. In this > case the slave device must not acknowledge the received byte. The master > upon detection of this condition must generate a STOP condition and > retry the transaction" > For I2C devices, the specification states [http://www.nxp.com/documents/user_manual/UM10204.pdf]: > "3.1.6 Acknowledge (ACK) and Not Acknowledge (NACK)" > "When SDA remains HIGH during this ninth clock pulse, this is defined as the Not > Acknowledge signal. The master can then generate either a STOP condition to > abort the transfer, or a repeated START condition to start a new transfer." Yes, that's exactly what I meant. The master has the choice, and the driver should not eliminate options here. > Let take a look on i2c/smbus xfer: > i2c_lock_adapter(adap) > adap->algo->master_xfer/smbus_xfer() > i2c_unlock_adapter(adap); > |- rt_mutex_unlock(&adapter->bus_lock); > |- task switch > > So, there is no guarantee that next xfer will address the same I2C client device, > which, in turn, may lead to BB detection (will lead to BB detection if previous > transfer has been not acknowledged by SMbus client device). That's a valid concern. > Small summary, I2C core + Davinci I2C driver provide ability to use repeated > start (Sr) only within one I2C transaction - which is a number of write/read > operations specified by i2c_msg array. NACK always interrupts transaction > with -EREMOTEIO. > > Also, the I2C core doesn't provide ability to manually send P. Hmm, Wolfram, what do you think? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
