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SubjectRe: Virtual to physical address mapping
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On Wed, 2002-09-18 at 14:06, Richard B. Johnson wrote:
> On 18 Sep 2002, Ole [ISO-8859-1] André Vadla [ISO-8859-1] Ravnås wrote:
>
> > Thanks, but the address specified there is certainly not the same as the
> > base address ifconfig reports. I made a simple program to verify this:
>
> [SNIPPED...]
>
> `ifconfig` reports the base address of a port (I don't know why).
> There are other addresses in use.

Ah.. that explains it all, as I modified net/core/dev.c earlier today to
report the base_addr present in the net_device structure in the
sprintf_stats() which is responsible for the /proc/net/dev output --
and, what I got was:
0xf88fa000
where the ifmap structure returned by the SIOCGIFMAP ioctl contained a
base_addr saying:
0xa000
I did this ugly hack (WRT net/core/dev.c) since I discovered that the
net_device()'s base_addr was an unsigned long, while ifmap's base_addr
was an unsigned short - and indeed, just like you said, it's only the
base-address that's returned in the ifmap. :-)

> eth0 Link encap:Ethernet HWaddr 00:50:DA:19:7A:7D
> inet addr:10.100.2.224 Bcast:10.255.255.255 Mask:255.0.0.0
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> RX packets:2630005 errors:0 dropped:0 overruns:0 frame:0
> TX packets:307396 errors:0 dropped:0 overruns:0 carrier:0
> collisions:2430 txqueuelen:100
> Interrupt:10 Base address:0xb800
>
> [SNIPPED...]
>
> A private version of `lspci` that actually reads the PCI ports
> shows:
>
> Device Vendor Type
> 0 Intel Corporation 440BX/ZX - 82443BX/ZX Host bridge
> [SNIPPED...]
> 11 3Com Corporation 3c905B 100BaseTX [Cyclone]
> IRQ 10 Pin A
> I/O ports : 0xb800->0xb87e
> I/O memory : 0xdf800000->0xdf80007f
>
> Notice that it has memory-mapped I/O.
> That said, neither of these addresses are the virtual addresses.
> On an ix86, these are physical addresses which are the same as
> the bus addresses. Other machines may not have the same physical
> and bus address. The virtual address is whatever mmap() returns
> in user-space, and whatever ioremap() returns in kernel space.
> Note that in kernel space, the returned value should not be used
> as a pointer. There are macros defined to access the I/O addressed
> elements. See .../linux/Documentation/IO-mapping.txt.

Ah, I see! Thanks a lot for your help! :-)

Best regards
Ole André


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