Date: Wed, 10 Jan 2001 19:23:04 -0800 From: Peter Wemm <peter@netplex.com.au> To: Mike Smith <msmith@FreeBSD.ORG> Cc: Jonathan Lemon <jlemon@flugsvamp.com>, Peter Jeremy <peter.jeremy@alcatel.com.au>, 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: <200101110323.f0B3N4Q64114@mobile.wemm.org> In-Reply-To: <200101110116.f0B1G8f00436@mass.osd.bsdi.com>
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Mike Smith wrote:
> > > > 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))
> > >
> > > This should be taken care of by the bus_space() macros; which is
> > > already done by most drivers in the tree. (Many drivers can run
> > > in either PIO or memory mapped mode)
> >
> > But the bus_space_() stuff doesn't handle changing register windows etc.
> > eg: if you have a 64K memory space and can read/write it directly when
> > memory mapped, but when on ISA it is all crammed into 16 lots of 4K windows
> > then bus_space_() cannot save you from this.
> >
> > ie:
> > if (IS_PCI(board_type)) {
> > value = *mem[reg];
> > } else {
> > if (board->window != window(reg))
> > board->window = window(reg);
> > value = inb(base + (reg % winsize));
> > }
>
> Typically, if you have half a clue, you will separate the ISA-aware parts
> of the driver from the PCI-aware parts and use a set of function vectors.
> Makes for much cleaner code. 8)
Yes, that is what Peter Jeremy said in the original email.. It can be
done but doesn't come for free. I was merely responding to the suggestion
to use the bus_space_ macros with a reason why they cannot be used in this
scenario to hide the different access methods. Yes, bus_space can be used
in the backend functions, but not at the top level driver.
Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5
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