cvs commit: src/sys/conf files src/sys/dev/uart uart_cpu.h uart_cpu_alpha.c uart_cpu_amd64.c uart_cpu_i386.c uart_cpu_ia64.c uart_cpu_pc98.c uart_cpu_sparc64.c uart_subr.c

[Marcel Moolenaar]

On Sat, Mar 20, 2004 at 12:00:27AM -0800, John-Mark Gurney wrote:
> Marcel Moolenaar wrote this message on Fri, Mar 19, 2004 at 18:14 -0800:
> >   The reasons for introducing these variables are:
> >   1.  Hints have side-effects. They reserve the unit number for use by
> >       isa or acpi devices and therefore cannot be used to select a pci
> >       device. Also, the use of a unit number to select a device prior
> 
> see below..  Hints are SUPPOSE to reserve a unit number of any bus...

> >       to bus enumeration is nonsense. The new variables have no side-
> >       effects and are not based on unit numbers.
> >   2.  Hints don't have the expression power to allow the sysadmin to
> >       select UARTs that are not legacy PC devices and need the support
> >       of compile-time constants to give the sysadmin some level of
> >       flexibility.
> 
> Hun? I don't follow this one?  Hints are suppose to be bus generic
> methods of tieing down any device on the subsystem so that you know
> exactly the correct device between reboots...  If PCI adn/or other
> busses don't understand hints, then this is a bug in the bus and
> should not introduce a new method of providing hints...

Hints are used to tell the kernel about possible devices in case
the kernel can not reliably detect them itself. This typically
applies to the ISA bus. Any bus that allows enumeration does not
need to have hints.

> >   The hw.uart.console and hw.uart.dbgport variables specify a list of
> >   attributes. An attribute is a tag-value pair, seperated by a colon.
> >   Attributes are seperated by a comma. Where possible, tags are the
> >   same as those in /etc/remote (only br and pa in practice). Details
> >   can be found in the manpage (not part of this commit).
> 
> I don't see how this prevents problems with probe order suddenly changing
> and you don't have the same console you thought you had...  also, how
> do you handle this before devfs is up?

Probe order is irrelevant if you specify the device by its I/O port
or memory mapped I/O address. When you need to pinpoint a device
prior to any form of bus enumeration, the unit number is meaningless
and any mechanism that includes a unit number is bogus. That's why
hints are the wrong tool for pinpointing a console or debug port.

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel at xcllnt.net