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i2c: Allow I2C devices to NAK start events

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Add a return value to the event handler.  Some I2C devices will
NAK if they have no data, so allow them to do this.  This required
the following changes:

Go through all the event handlers and change them to return int
and return 0.

Modify i2c_start_transfer to terminate the transaction on a NAK.

Modify smbus handing to not assert if a NAK occurs on a second
operation, and terminate the transaction and return -1 instead.

Add some information on semantics to I2CSlaveClass.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Corey Minyard 2017-01-09 11:40:20 +00:00 • committed by Peter Maydell
parent ffe22bf510
commit d307c28ca9
14 changed files with 79 additions and 26 deletions
Download patch file Download diff file Expand all files Collapse all files

33
hw/i2c/core.c
View file

@ -88,18 +88,26 @@ int i2c_bus_busy(I2CBus *bus)
return !QLIST_EMPTY(&bus->current_devs);
}
/*
* Returns non-zero if the address is not valid. If this is called
* again without an intervening i2c_end_transfer(), like in the SMBus
* case where the operation is switched from write to read, this
* function will not rescan the bus and thus cannot fail.
*/
/* TODO: Make this handle multiple masters. */
/*
* Start or continue an i2c transaction. When this is called for the
* first time or after an i2c_end_transfer(), if it returns an error
* the bus transaction is terminated (or really never started). If
* this is called after another i2c_start_transfer() without an
* intervening i2c_end_transfer(), and it returns an error, the
* transaction will not be terminated. The caller must do it.
*
* This corresponds with the way real hardware works. The SMBus
* protocol uses a start transfer to switch from write to read mode
* without releasing the bus. If that fails, the bus is still
* in a transaction.
*/
int i2c_start_transfer(I2CBus *bus, uint8_t address, int recv)
{
BusChild *kid;
I2CSlaveClass *sc;
I2CNode *node;
bool bus_scanned = false;
if (address == I2C_BROADCAST) {
/*
@ -130,6 +138,7 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, int recv)
}
}
}
bus_scanned = true;
}
if (QLIST_EMPTY(&bus->current_devs)) {
@ -137,11 +146,21 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, int recv)
}
QLIST_FOREACH(node, &bus->current_devs, next) {
int rv;
sc = I2C_SLAVE_GET_CLASS(node->elt);
/* If the bus is already busy, assume this is a repeated
start condition. */
if (sc->event) {
sc->event(node->elt, recv ? I2C_START_RECV : I2C_START_SEND);
rv = sc->event(node->elt, recv ? I2C_START_RECV : I2C_START_SEND);
if (rv && !bus->broadcast) {
if (bus_scanned) {
/* First call, terminate the transfer. */
i2c_end_transfer(bus);
}
return rv;
}
}
}
return 0;