Modules and Buses

[M. Warner Losh]

In message: <20100825105908.c8b626fd.ray at dlink.ua>
            Alexandr Rybalko <ray at dlink.ua> writes:
: On Mon, 23 Aug 2010 22:12:59 -0600 (MDT)
: "M. Warner Losh" <imp at bsdimp.com> wrote:
: 
: >> In message: <20100819170643.38362078.ray at dlink.ua>
: >>             Alexandr Rybalko <ray at dlink.ua> writes:
: >> : On Thu, 19 Aug 2010 09:18:46 -0400
: >> : John Baldwin <jhb at freebsd.org> wrote:
: >> : 
: >> : >> On Thursday, August 19, 2010 8:38:05 am Alexandr Rybalko wrote:
: >> : >> > Hi all,
: >> : >> > 
: >> : >> > Can someone say, how `make` in sys/modules dir can obtain available buses.
: >> : >> > I try to make clean version of bfe, that can be for PCI bus or can be part 
: >> : >> of SoC (like BCM5354) on SSB bus.
: >> : >> > So for proper module building I need to know what bus interface I must build 
: >> : >> if_bfe_pci.c, or if_bfe_siba.c, or both?
: >> : >> 
: >> : >> You can always include both buses.  If a bus driver isn't present in the 
: >> : >> kernel the attachment will just never be invoked.
: >> : 
: >> : I was afraid of such response. Now I have to rewrite siba implementation to newbus :)
: >> : Thanks you for answer! 
: >> 
: >> In the module building system (modules built with sys/modules
: >> Makefiles), we generally include all relevant busses.  So, for i386 we
: >> include EISA front ends for some devices, but omit that on amd64.  For
: >> siba, you'd only include it on mips, since that's the only platform
: >> where this would be relevant (I know broadcom wireless drivers are
: >> implemented via a pci <-> siba bridge, but that's a really special
: >> case).
: >> 
: >> Check out sys/modules/ep for an example from the mists of history..
: >> 
: >> Warner
: 
: Thanks you Warner,
: 
: I believe Broadcom wifi cards not last instance of Broadcom devices with PCI-to-SSB bridge.
: Since this is modular platform that can join multiple already existence chips onto biggest chip.
: And SSB is spacial case of OCP bus, who can be used not only for MIPS periphery, but ARM too.
: 
: So I think I should implement the SSB as a full functional bus.

I agree we should implement it as a full functional bus.  It would
save a little code to only compile on mips.  There's no arm ssb
implementation in the tree, and the use case on non-mips is still
theoretical.  On the other hand, the bus attach code is small, and so
would have little impact being always in the module.  So I could go
either way with this, due to the limitations in our module system.

Warner