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List:       freebsd-hackers
Subject:    Re: What tty changes - question on porting ltmdm and hcfmdm to
From:       Ted Mittelstaedt <tedm () mittelstaedt ! us>
Date:       2010-04-24 18:22:33
Message-ID: 4BD336E9.5070007 () mittelstaedt ! us
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On 4/24/2010 8:29 AM, M. Warner Losh wrote:
> In message:<20100424102255.12d782f8@ernst.jennejohn.org>
>              Gary Jennejohn<gljennjohn@googlemail.com>  writes:
> : On Fri, 23 Apr 2010 16:27:12 -0700
> : Ted Mittelstaedt<tedm@mittelstaedt.us>  wrote:
> :
> :>    Setting aside the question of why do we break software that a lot of
> :>  people use
> :>  (these chips are in use on a lot of laptops) is there a document
> :>  somewhere that explains
> :>  what changes need to be made in code for this new tty setup?  Or, is
> :>  there a set
> :>  of magic include files or a "conversion shim" library that will allow
> :>  these kinds
> :>  of programs to build without much work?
> :>
> :>    Or is porting these drivers just so non-trivial that the only way is
> :>  to just delve into
> :>  the system manuals and delve into the driver code and try to figure out
> :>  what is
> :>  going on in each?  If that's the case that's probably beyond my ability
> :>  but I'd
> :>  be happy to serve as a testbed.
> :>
> :
> : The guy to ask about this would be Ed Schouten (ed@). AFAICR he did the new
> : TTY stuff.  I don't know whether he reads these lists.
> :
> : AFAIK there is no easy way to fix this and there are no backwards compati-
> : bilty shims or magic header files.
> :
> : The fundamental problem with ltmdm is that it's a KLD and has to grovel
> : around in the guts of the kernel.  That makes fixing it decidely non-
> : trivial.
>
> The fundamental reason that things changed was due to the locking of
> the TTY layer.  These things change over time, and the old APIs made
> it very difficult to lock without driver visible changes.
>
> Warner
>    

I mailed Ed and his response is to look at the changelog of 
sys/dev/uart/uart_tty.c for an
idea of how to rewrite the driver, so I will take a look there.  The 
ltmdm driver was
updated in 2008 for an early version of FreeBSD 8, before the TTY layer 
changes went
in, so that's where I'll start.

Ted
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