Re: b43 depends on lots of modules

[Larry Finger <Larry.Finger@lwfinger.net>]

Jan Engelhardt wrote:
> 
> It's because the Kconfig description says SSB is for embedded systems,
> come thinking WRT54, so I wondered what exactly requires SSB.
> Is it some bus within the wireless chip itself?

That isn't quite what Kconfig says, which is

config SSB
        tristate "Sonics Silicon Backplane support"
        depends on SSB_POSSIBLE
        help
          Support for the Sonics Silicon Backplane bus.
          You only need to enable this option, if you are
          configuring a kernel for an embedded system with
          this bus.
          It will be auto-selected if needed in other
          environments.

          The module will be called ssb.

          If unsure, say N.


The text says that it will be auto-selected if needed for other
environments, and it will be for PCI-based BCM43XX devices.

Most, if not all, Broadcom devices consist of several cores of
different types that are interconnected by a Sonics Silicon Backplane
(ssb). On a BCM43XX device, two of these will be an IEEE 802.11 core
plus at least one bus interface. For example, in the BCM4312 now in my
machine I get

ssb: Core 0 found: ChipCommon (cc 0x800, rev 0x16, vendor 0x4243)
ssb: Core 1 found: IEEE 802.11 (cc 0x812, rev 0x0F, vendor 0x4243)
ssb: Core 2 found: PCMCIA (cc 0x80D, rev 0x0A, vendor 0x4243)
ssb: Core 3 found: PCI-E (cc 0x820, rev 0x09, vendor 0x4243)

As my device does not have a PCMCIA interface, that core is presumably
not attached, but the other 3 are active.

Before b43 was developed, all communications between the 802.11 core
and the PCI bus were handled by bcm43xx; however, that scheme meant
that code had to be duplicated for 3 different drivers. By splitting
out that part of the code, b43, b43legacy and b44 can share
considerable code. That is the module named ssb.

Larry