i386/100831: sio ignores BIOS information about serial ports - bounty offered

[Marcel Moolenaar]

The following reply was made to PR i386/100831; it has been noted by GNATS.

From: Marcel Moolenaar <marcel at xcllnt.net>
To: Bruce Evans <bde at zeta.org.au>
Cc: Jo Rhett <jrhett at svcolo.com>, njl at freebsd.org,
        freebsd-gnats-submit at freebsd.org, freebsd-i386 at freebsd.org
Subject: Re: i386/100831: sio ignores BIOS information about serial ports - bounty offered
Date: Wed, 2 Aug 2006 13:33:19 -0700

 On Aug 2, 2006, at 12:32 PM, Bruce Evans wrote:
 
 > On Wed, 2 Aug 2006, Jo Rhett wrote:
 >
 >>> On Wed, 2 Aug 2006, Jo Rhett wrote:
 >>>> 1. We can't/won't fix the sio0<->sio1 problem because fixing  
 >>>> ACPI is hard
 >>
 >> On Aug 2, 2006, at 10:25 AM, Bruce Evans wrote:
 >>> _I_ can't/won't fix it because not just the above :-).  Swapping  
 >>> of consoles
 >>> only could be fixed within the driver (so that ACPI is not  
 >>> involved and
 >>> you don't have to change device.hints) since consoles have to be  
 >>> hard-wired
 >>> in some way and the hints are good enough for wiring the unit  
 >>> number to
 >>> the i/o address (provided it's an old ISA port -- otherwise hints  
 >>> based
 >>> on the i/o address don't work).
 >>
 >> Sorry, color me dumb.  I'm getting lost here.  The problem I was  
 >> observing is that device hints is being (mostly) ignored by ACPI  
 >> and thus this is the root problem to fix.  I'm not sure what  
 >> you're trying to say here.
 >
 > Console drivers have to and do use the hints directly so as to work  
 > before
 > bus stuff like ACPI is initializated.
 
 It is a mistake for console drivers to use the hints. It's a mistake
 even to use hints for anything else. The fundamental problem with hints
 is that they use a device numbering for identification. This is totally
 wrong for low-level consoles, because device numbers mean nothing at
 that time and are mostly wrong during bus enumeration, because you
 cannot generally predict device numbers.
 
 Low-level console drivers should only use I/O port or memory mapped I/O
 information to get to the hardware and hints for non-enumerating busses
 should only provide resource information. During bus enumeration this
 will eventually be mapped to device numbers and one can establish the
 logical connection between low-level consoles and high-level devices.
 
 Thus: hints are not hints, but a convoluted mix of enforced settings
 and suggestions that are partially and inconsistently used and there-
 fore much sooner the cause of problems that a solution to it.
 
 -- 
   Marcel Moolenaar         USPA: A-39004          marcel at xcllnt.net