puc(4) man page update?

[John Baldwin]

On Friday 04 July 2008 03:31:41 pm Marcel Moolenaar wrote:
> 
> On Jul 4, 2008, at 2:59 AM, Dmitry Morozovsky wrote:
> 
> > doesn't splitting uart out of kernel broke serial console? Last time  
> > I checked
> > it did.
> 
> Yes, it does. The serial console is setup/initialized and
> used before pre-loaded modules are linked and/or usable.
> We don't have the support in place that allows you to boot
> without console until pre-loaded modules are initialized,
> at which time add a low-level console device is setup.
> It's not that hard to do, I think.
> 
> So, currently low-level console drivers, such as dcons(4),
> sio(4) and uart(4) need to be compiled into the kernel.
> Consequently any devices/busses to which any of these can
> attach must be compiled into the kernel as well. Of these
> acpi(4) and puc(4) are good examples. acpi(4) is a good
> example because we use hints to work around the issue and
> have sio(4) attach to isa(4) instead...

Actually, sio does attach to acpi0.  What happens for sio is that the 
low-level console stuff is just doing bare-bones inb/outb anyway.  sioX 
devices do attach to acpi0 though just fine.  Note that in the common case 
acpi is a module on i386 yet it still manages to work fine. :)

Also note that the hints for sio0 aren't actually used, just the 'flags' are 
applied.  Thus, you can have:

hint.sio.0.at="isa0"
hint.sio.0.port="0x3f8"
hint.sio.0.irq="4"
hint.sio.0.flags=0x10

But if ACPI lists COM2 before COM1 in the namespace you end up with:

sio0 at port 0x2f8 irq 3 (used as serial console!)
sio1 at port 0x3f8 irq 4

This is why I wanted to wire devices using the resources in hints so that 
people would reliably get a serial console on COM1 == sio0 with the existing 
hints.  As it is, people have to engage in far uglier hacks currently since 
there is no in-tree solution.

-- 
John Baldwin