lkml.org 
[lkml]   [2001]   [Oct]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
Subjectioremap() vs. ioremap_nocache()
Jes Sorensen was kind enough to point out a longstanding
mis-conception that I had about ioremap(): I thought that ioremap()
was being deprecated in favor of ioremap_nocache() because the former
does not clearly define what kind of memory attribute will be used to
access the mapped memory (cached, write-through cached,
write-coalescing, etc). But I seem to have been wrong about that.
Now, as far as I know, on x86, ioremap() will give write-through
cached mappings (in the absence of mtrr games). If this is true, how
can this work? There are many drivers out there that use ioremap() on
memory mapped I/O regions that do NOT have the "Prefetchable" bit set
in the PCI BAR. For example, the eepro100 driver does this and it has
a routine called wait_for_cmd_done(), which spins on an ioremapped
read. On an x86, what prevents these reads from being cached?

Thanks,

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

\
 
 \ /
  Last update: 2005-03-22 13:04    [W:0.074 / U:0.836 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site