lkml.org 
[lkml]   [1998]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Non-page-aligned PCI base address


On Tue, 24 Nov 1998, Martin Mares wrote:

> Hi,
>
> > Does anybody has an idea how to fix above ? I couldn't find anything about
> > it in any docs/code. The box where my kernel module was tested (AMI
> > Motherboard Goliath II PCI/EISA) has 7 PCI slots on 2 buses (that means,
> > probably too much), and by some cards I got
> >
> > this strange base 0 addr: 0xfebffd80 (as found in pci_dev->base_address[0];
> > ^^^
> > The size of base0 is 0x80. Is it possible that bios makes some attempts
> > to 'save' address space, being too pedantic ?
> >
> > This is bad if I want to perform ioremap() to access control registers of
> > the card through mapped memory (needed in ISR for IRQ status/config regs
> > access). The kernel where it was tested was 2.1.108. Momentary, I'm
> > aligning the address to the nearest bottom page and ioremap it, keeping
> > track of the address offset when accessing it. But is sucha thing realy
> > necessary ?
> >
> > Please cc my address if you got some answer, as I'm not subscribed here.
>
> This seems to be perfectly correct -- PCI just states every memory / I/O
> region has to be aligned to a multiple of its size and that the size is
> a power of two >= 16 (memory) or 4 (I/O). Therefore you cannot expect
> memory regions smaller than 4K to be page-aligned.
>
> Anyway, can you send me lspci -vvx output for this device?
>


Yeah, but ioremap() on x86 fails when the physical address you request to
remap is not page-aligned. It doesn't on Sparc/Alpha and PPC AFAICT from
a cursory reading of the code since all the PCI memory space is mapped.

I consider this as both a bug and a feature :-):

- the bug: PCI spcifications dor not require it,
- the feature: if you use mmap to PCI space from user mode like X does, it
is better to have at most one device per page, and in this case the
device area can always be page aligned.

Gabriel.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:45    [from the cache]
©2003-2011 Jasper Spaans