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Re: Should /dev/kmem support above 0x80000000 area?

To: Jun Sun <>
Subject: Re: Should /dev/kmem support above 0x80000000 area?
From: Guido Guenther <>
Date: Mon, 11 Dec 2000 19:56:30 +0100
In-reply-to: <>; from on Mon, Dec 11, 2000 at 06:26:51PM -0800
References: <> <> <> <>
User-agent: Mutt/1.2.5i
On Mon, Dec 11, 2000 at 06:26:51PM -0800, Jun Sun wrote:
> Guido Guenther wrote:
> > 
> > On Mon, Dec 11, 2000 at 12:28:19PM +0100, Maciej W. Rozycki wrote:
> > > friends) by glibc.  At least XFree86 and SVGATextMode make use of these
> > > features.  I suppose it's the same for MIPS (I haven't checked, though).
> > Yes. xf86MapVidMem & friends use /dev/mem to mmap videomemory & iospace
> > independent of architecure.
> >  -- Guido
> I am surprised.  I thought /dev/mem is for accessing SYSTEM RAM.  (do a 'man'
I'd not call it system ram but rather ''visible address space'' or
something. If there's actually ''system ram'' or the fb of a graphics
card at a given address doesn't make a difference.

> on /dev/mem)  It is also confirmed by the code in drivers/char/mem.c.  If you
> want to access anything beyond 'high_memory", nothing is read.  
> Note that drivers/char/mem.c is cross-platform code.  I am not sure how X
> would access video memory through /dev/mem on either MIPS or other platforms.
The newports REX3 for example is at (KSEG1 + 0x1f0f000) which is mmaped
by the xserver to access the REX3s registers.
 -- Guido

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