From owner-freebsd-arch  Fri Jan 19  6: 5:55 2001
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Date: Fri, 19 Jan 2001 15:04:57 +0100
From: Eivind Eklund <eivind@FreeBSD.ORG>
To: Peter Jeremy <peter.jeremy@alcatel.com.au>
Cc: Brian Somers <brian@Awfulhak.org>,
	Sergey Babkin <babkin@FreeBSD.ORG>, freebsd-arch@FreeBSD.ORG
Subject: Re: cvs commit: src/sys/gnu/i386/isa dgb.c dgm.c dgmreg.h dgreg.h
Message-ID: <20010119150457.A18464@thinksec.com>
References: <babkin@FreeBSD.org> <200101052146.f05LkDi49430@hak.lan.Awfulhak.org> <20010111064126.A10214@pc0640.alcatel.com.au>
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In-Reply-To: <20010111064126.A10214@pc0640.alcatel.com.au>; from peter.jeremy@alcatel.com.au on Thu, Jan 11, 2001 at 06:41:26AM +1100
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On Thu, Jan 11, 2001 at 06:41:26AM +1100, Peter Jeremy wrote:
> On Fri, Jan 05, 2001 at 09:46:13PM +0000, Brian Somers wrote:
> >I have the a driver that will replace dgb and dgm and support a bunch 
> >of other digiboards.  Now all I need is the time to add back the 
> >{E,}ISA probe routines.
> 
> There are come significant differences between the [E]ISA aand PCI
> DigiBoards:
> - The [E]ISA cards use I/O ports whilst the PCI boards use
>   memory-mapped registers.
> - The PCI cards have a flat 4MB window.  The [E]ISA cards access
>   on-board memory via a 8KB or 32KB window.
> 
> This means that the code does a lot of checking to see if the card
> is PCI or not, resulting in expressions like:
> 	((IS_PCI(board_type)) ? *mem[reg] : inb(base + reg))
> 
> The Linux driver (maintained by Digi) uses (the equivalent of) virtual
> functions for all card accesses.
> 
> Both these approaches add run-time overheads and can adversely affect
> code legibility.

The technique I've used for similar cases is to do the access through macros,
putting the main source in a separate file, and having one "main source"
that use the macros, and is included in two separate files that define
separate macros.

Ie, something like

dgb_pci.c:
#define GETDATA(mem, base, reg) (*mem[reg])
#include "dbg_main.c"

dgb_eisa.c:
#define GETDATA(mem, base, reg) inb(base + reg)
#include "dgb_main.c"

... with dgb_main.c just using GETDATA() for accesses.  (This is just based
on the above problem description, not any knowledge of the DigiBoard.  And
GETDATA is probably not the right name.)

Eivind.


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