Re: [Qemu-devel] [PATCH V2 2/7] i2c: implement broadcast write.

[Frederic Konrad]

On 24/06/2015 08:35, Peter Crosthwaite wrote:
> On Mon, Jun 15, 2015 at 8:15 AM,  <address@hidden> wrote:
> > From: KONRAD Frederic <address@hidden>
> >
> > This does a write to every slaves when the I2C bus get a write to address 0.
> >
> > Signed-off-by: KONRAD Frederic <address@hidden>
> > ---
> >   hw/i2c/core.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 45 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/i2c/core.c b/hw/i2c/core.c
> > index 5a64026..db1cbdd 100644
> > --- a/hw/i2c/core.c
> > +++ b/hw/i2c/core.c
> > @@ -15,6 +15,7 @@ struct I2CBus
> >       I2CSlave *current_dev;
> >       I2CSlave *dev;
> >       uint8_t saved_address;
> > +    bool broadcast;
> >   };
> >
> >   static Property i2c_props[] = {
> > @@ -67,6 +68,8 @@ I2CBus *i2c_init_bus(DeviceState *parent, const char *name)
> >
> >       bus = I2C_BUS(qbus_create(TYPE_I2C_BUS, parent, name));
> >       vmstate_register(NULL, -1, &vmstate_i2c_bus, bus);
> > +
> > +    bus->broadcast = false;
> 0 initialiser should not be needed for new QOM object.
>
> >       return bus;
> >   }
> >
> > @@ -89,6 +92,21 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, int 
> > recv)
> >       I2CSlave *slave = NULL;
> >       I2CSlaveClass *sc;
> >
> > +    if (address == 0x00) {
> > +        /*
> > +         * This is a broadcast.
> > +         */
> One line comment.
>
> > +        QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
> > +            I2CSlave *dev = I2C_SLAVE(kid->child);
> > +            sc = I2C_SLAVE_GET_CLASS(dev);
> > +            bus->broadcast = true;
> Move outside loop.
>
> > +            if (sc->event) {
> > +                sc->event(dev, recv ? I2C_START_RECV : I2C_START_SEND);
> > +            }
> > +        }
> > +        return 0;
> > +    }
> > +
> >       QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
> >           DeviceState *qdev = kid->child;
> >           I2CSlave *candidate = I2C_SLAVE(qdev);
> > @@ -114,9 +132,21 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, int 
> > recv)
> >
> >   void i2c_end_transfer(I2CBus *bus)
> >   {
> > +    BusChild *kid;
> >       I2CSlave *dev = bus->current_dev;
> >       I2CSlaveClass *sc;
> >
> > +    if (bus->broadcast) {
> > +        QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
> > +            I2CSlave *dev = I2C_SLAVE(kid->child);
> > +            sc = I2C_SLAVE_GET_CLASS(dev);
> > +            if (sc->event) {
> > +                sc->event(dev, I2C_FINISH);
> > +            }
> > +        }
> > +        bus->broadcast = false;
> > +    }
> > +
> >       if (!dev) {
> >           return;
> >       }
> > @@ -131,8 +161,22 @@ void i2c_end_transfer(I2CBus *bus)
> >
> >   int i2c_send(I2CBus *bus, uint8_t data)
> >   {
> > +    BusChild *kid;
> >       I2CSlave *dev = bus->current_dev;
> >       I2CSlaveClass *sc;
> > +    int ret = 0;
> > +
> > +    if (bus->broadcast) {
> > +        QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
> > +            I2CSlave *dev = I2C_SLAVE(kid->child);
> > +            sc = I2C_SLAVE_GET_CLASS(dev);
> > +            bus->broadcast = true;
> > +            if (sc->send) {
> > +                ret |= sc->send(dev, data);
> > +            }
> > +        }
> Still not sure about the duped core functionality of each of these
> APIs. That is, the same code is needed in both a looped form and a 1
> form. Can this be solved by listifying current_dev? That is, ->current
> dev is turned into a list which in the normal case will be populated
> with 1 element by start_transfer() for the current dev. In the
> broadcast case, all qbus.children are added to the list. The broadcast
> bool is then removed. start() send() and end_transfer() then just loop
> through the list unconditionally.

I think better keeping this broadcast as we need it for VMSD anyway?

> Regards,
> Peter
>
> > +        return ret;
> > +    }
> >
> >       if (!dev) {
> >           return -1;
> > @@ -151,7 +195,7 @@ int i2c_recv(I2CBus *bus)
> >       I2CSlave *dev = bus->current_dev;
> >       I2CSlaveClass *sc;
> >
> > -    if (!dev) {
> > +    if ((!dev) || (bus->broadcast)) {
> >           return -1;
> >       }
> >
> > --
> > 1.9.0