newbus questions

[Milan Obuch]

On Thursday 16 March 2006 13:06, Artem 'ZaZooBred' Ignatiev wrote:

...

> > > 2. SAA7146 uses I2C to communicate with tuners, and I know that there
> > > are some I2C-related peaces already in kernel. I would like to reuse
> > > that code, if possible, but can't figure out where to look and how to
> > > link it in.
> >
> > There is some basis for i2c, look in /usr/src/sys/dev/iicbus directory.
> > There are two kinds of i2c controllers - bit banged and full hardware
> > controlled. The former is easily usable, you need just set and query
> > methods implementation (look into iicbb_if.m), even if this has not the
> > full i2c potential, the latter is (at least for me) somewhat hard to
> > understand. I tried to implement such driver with Geode's Access.BUS
> > controller, but so far no luck. And no description, google does not help
> > me either.
> > If SAA7146 uses bit banging interface or can be forced into such mode,
> > you can do it in small amount of time.
>
> I had looked at both iicbb_if.m and iicbus_if.m.
> SAA has internal logic to handle IIC, so iicbb was of no interest to me.
> As to iicbus_if.m, it way closer to what I want.

i2c subsystem in FreeBSD is somewhat SMBus oriented. Look at iicsmb, smbus and 
smb manpages. iicbus class implements just basic primitives.

> It looks like linux is one layer of abstraction higher, so they have
> "send N i2c messages" kind of functions, and in case of these cards,
> logic is like that:
> get array of messages, pack them into dwords, transfer that dwords using
> DMA to card, read that dwords back and decode them into response. All
> START/STOP conditions are handled by SAA chip itself, and I hoped that
> there was something similar in other drivers, so there's no need to
> reinvent the wheel for me.

There is substantial difference - FreeBSD is modularised, linux (and NetBSD 
and OpenBSD as well, if I looked there at rught places) somehow makes i2c 
drivers monolithic, with code duplicated over all drivers. FreeBSD lacks this 
'top-level' i2c-exec function.

> > > 3. Card vendors use different PCI_SUBDEVICE on SAA7146 to indicate
> > > which tuner is (possibly) used. So, I suppose that "bus"-driver shall
> > > provide some way to tuner-driver to get this information. How that can
> > > be done?
> >
> > This is not that easy to understand at first, but bus 'ivars' are
> > intended for this purpose. man device_get_ivars would be first step as it
> > was for me to understand this.
>
> Yeah, that told me to look into BUS_READ_IVAR(9), and it looks like
> something I can use, so now my question is reformed to ``how can I from
> child driver get the bus device_t''.
>

Look into bus_if.m - child devices are added using device_add_child. And there 
is device_get_parent... Oh, and maybe pcf device is similar to SAA7146 and 
may give you an idea on i2c driver implementation...

Regards,
Milan

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